Heart arrhythmia and palpitations: what a racing, fluttering, or irregular heartbeat means — and when it's dangerous

Short Answer

An arrhythmia is a problem with the heart's electrical timing: the beat runs too fast, too slow, or irregularly. Palpitations are what that can feel like — racing, pounding, fluttering, or skipped beats. Most are harmless. Fainting, chest pain, or breathlessness with them are not, and need urgent care.

A heart arrhythmia means the heart’s electrical timing is off: the beat may be too fast, too slow, or erratic. In adults, a tachycardia heart rate is generally more than 100 beats per minute, while bradycardia is generally less than 60 beats per minute — though sleep, fitness, medications, and symptoms all change what that number means for you. Palpitations are the feeling of that beat breaking through your normal body “background noise”: racing, pounding, fluttering, flip-flopping, or skipped beats felt in your chest, throat, or neck. (heart.org)

Most palpitations are brief and not dangerous, especially when they show up after stress, anxiety, exercise, caffeine or other stimulants, hormone shifts, dehydration, poor sleep, or low blood sugar. That does not mean they are imaginary. It means your heart, nervous system, hormones, fluids, and electrolytes can all change how forcefully or noticeably your heart beats. But palpitations can also be the symptom you feel when an actual rhythm disorder is happening underneath. (mayoclinic.org)

Rhythm matters because the heart is a pump with timing. If the electrical signal is too fast, too slow, or chaotic, the chambers may not fill or squeeze efficiently, so less blood may reach your brain, lungs, and other organs. The most common sustained rhythm disorder illustrates why this can matter: "Atrial fibrillation represents the most prevalent cardiac arrhythmia and is associated with substantial morbidity, including an increased risk for stroke and heart failure". Current AHA/ACC/HRS guidance also describes atrial fibrillation as the most common sustained arrhythmia and links it with higher risks of stroke and heart failure. (ahajournals.org)

So the short version is: if palpitations come with chest pain or pressure, fainting, severe shortness of breath, or severe dizziness, call emergency services now — 911 in the U.S. If the irregular, very fast, or very slow heartbeat keeps coming back, lasts longer than usual, or feels different from your normal, get it checked. A clinician confirms an arrhythmia with an ECG/EKG, Holter monitor, event recorder, or another medical heart-rhythm test — not by a wearable or wellness app alone. (mayoclinic.org)

If you have been told this is anxiety and you are still not convinced: you are not imagining it, and noticing your own heartbeat does not make you a hypochondriac. Palpitations are one of the most common reasons people see a clinician about their heart, most of them turn out not to be dangerous, and some of them do matter — which is exactly why the honest answer is to check the pattern rather than to reassure you or alarm you from a distance.

What is an arrhythmia?

In a normal heartbeat, an electrical signal starts in the sinus node — the heart’s natural pacemaker — and travels through the heart in an organized sequence, so the chambers squeeze in the right order. For most adults, a normal resting heart rate is roughly 60–100 beats per minute. A tachycardia heart rate means the heart is beating too fast at rest — typically over 100 bpm — but rate is only one part of rhythm. An arrhythmia is what happens when the heart’s electrical signaling stops following its usual pattern: the signal may fire too fast, too slowly, from the wrong place, or along an abnormal pathway, making the heartbeat fast, slow, irregular, or unexpectedly “skippy.” (heart.org)

A palpitation is different. It is the feeling of your heartbeat — racing, fluttering, pounding, skipping, or thudding — not a diagnosis by itself. You can feel palpitations while your actual rhythm is normal, especially when your nervous system is activated, you’re lying still, or you’re paying close attention to your body. And the reverse can also happen: some arrhythmias cause few symptoms or none at all, so you may not feel anything unusual even when the rhythm is abnormal. (my.clevelandclinic.org)

That gap between what people feel and what the rhythm actually is is exactly why palpitations get investigated: "Palpitations may relate to severe arrhythmias, resulting in life-threatening events or cardiac death" — most are benign, but the sensation alone can’t tell you which is which. An ECG, Holter, or event monitor can record the heart’s electrical activity and show whether symptoms line up with an arrhythmia. (heart.org)

Types of arrhythmia

Clinicians usually sort arrhythmias in two practical ways: how fast the heart is going and where the electrical signal starts. That matters because the same sensation — a racing, fluttering, skipping, or thudding heartbeat — can come from very different rhythms. Some start in the upper chambers, some in the lower chambers, some are single “early” beats, and some are sustained rhythms that need urgent care. The table below is only a map, not a diagnosis or treatment guide.

Use this section as the overview layer: names, body-feel, and why location matters. Detailed diagnosis, stroke-risk scoring, medications, procedures, and emergency treatment belong on the dedicated AFib, SVT, PVC, and arrhythmia treatment pages — not in this general map.

Why do I feel palpitations — and why at night or lying down?

Palpitations are the feeling of your heartbeat becoming noticeable: racing, pounding, fluttering, skipping, or beating “wrong.” That sensation can come from a normal heart beating harder than usual, a premature beat, anxiety physiology, or a true rhythm problem — so the feeling itself is not a diagnosis. Common, usually benign triggers include caffeine, alcohol, nicotine, stress or panic, intense exercise, fever, dehydration, poor sleep, low blood sugar or electrolyte shifts, some cold/asthma/thyroid/heart medicines, stimulant drugs, and hormonal changes. If you’re searching “heart palpitations when lying down” or “heart racing at night,” these triggers are often the first place clinicians look — especially when the episodes are brief and you otherwise feel well. (mayoclinic.org)

Palpitations often feel louder at night because your body finally gets quiet. During the day, movement, screens, conversations, and tasks compete for attention; in bed, there is less noise for your brain to process, so every thump has more room to register. Cleveland Clinic and Johns Hopkins both describe this pattern: people may feel the same skipped or pounding beats more when they’re lying in bed with nothing distracting them. Position can matter too. Lying on your side or curled up can increase pressure in the chest or body for some people, and a change of position — rolling over, sitting up, or walking slowly around the room — may make the sensation fade. (my.clevelandclinic.org)

Late-evening body mechanics can stack the odds. A big meal, alcohol, nicotine, chocolate, caffeine too late in the day, dehydration, reflux, or going to bed wired and underslept can all converge at the same time you lie down. That does not mean the “irregular heartbeat at night” is automatically dangerous; it means bedtime can be the moment when your nervous system, digestion, hydration status, and heart rhythm become noticeable all at once. There is no single “best sleeping position for heart palpitations” that works for everyone. If one side makes the pounding worse, try rolling to the other side, elevating your head slightly if reflux is part of the picture, or sitting up and breathing slowly. If your heart often races when you lie down, it’s worth scheduling a clinician visit rather than trying to solve it with sleep position alone. (my.clevelandclinic.org)

Hormones can change the pattern, too. Some people notice palpitations before a period, during pregnancy, or around menopause, because shifts in hormones, blood volume, stress response, sleep, and temperature regulation can make the heart feel more reactive. Mayo Clinic lists hormone changes linked with menstruation, pregnancy, and menopause among common causes of palpitations; Cleveland Clinic notes that palpitations in pregnancy are common and usually harmless, but they should still be mentioned to your pregnancy clinician — especially if they are new, frequent, worsening, or paired with dizziness, chest pain, fainting, or trouble breathing. (mayoclinic.org)

What helps depends on the “why.” If you can see a pattern — palpitations after coffee, alcohol, nicotine, dehydration, poor sleep, a heavy meal, or a stressful day — reducing that trigger is more useful than chasing a one-size-fits-all fix. Slow breathing, relaxation practices, hydration when you’re dry, and changing position may calm some benign episodes. Vagal maneuvers are sometimes used for certain fast rhythms, but they’re not a DIY diagnosis tool; if your episodes are strong, recurrent, or new, ask a clinician what is safe for you. (my.clevelandclinic.org)

And no: there isn’t a proven “vitamin that stops heart palpitations” for everyone. Electrolyte problems — including potassium, sodium, or magnesium imbalance — can contribute to palpitations, and blood work can sometimes reveal anemia, thyroid problems, vitamin deficiency, or electrolyte imbalance. But taking supplements blindly can backfire, especially with potassium or if you have kidney disease, take blood pressure/heart medicines, or are pregnant. If a true deficiency is found, correcting it is a clinician’s call; persistent palpitations deserve an ECG-based evaluation, not a supplement experiment. (heart.org)

When is an arrhythmia dangerous? "Can it kill you?"

Most palpitations are not dangerous, and many abnormal rhythms turn out to be harmless once a clinician documents what the heart is actually doing. The danger is not decided by how dramatic the flutter feels. It depends on the rhythm type, whether your heart is structurally healthy, how fast or slow the rhythm is, and what happens to blood flow while it’s happening. A run of beats from the lower chambers can be serious because the ventricles are the part of the heart that pushes blood to the body; ventricular fibrillation is an emergency because the heart can stop pumping effectively, and ventricular tachycardia can also become an emergency, especially in people with heart disease. AFib is usually not a “drop dead right now” rhythm, but it can let blood pool and clot in the heart, raising stroke risk over time if it is not recognized and managed. A very slow rhythm can be dangerous too if it drops blood flow enough to cause near-fainting or fainting. That’s why the real question is not only “is tachycardia dangerous?” or “can arrhythmia kill you?” — it’s “what rhythm is this, in what body, with what symptoms?” (heart.org)

Duration and persistence matter because they change the odds that this is more than a brief skipped beat. A one-off flutter that lasts a few seconds is different from a fast, irregular, or pounding heartbeat that lasts for hours, keeps returning, or shows up every day for days or weeks. There is no magic “3 days” cutoff that makes palpitations dangerous, but palpitations that continue for an hour or more, suddenly become more frequent, happen all day, or keep recurring deserve medical evaluation — usually with an ECG or a monitor that can catch the rhythm while it is happening. If palpitations come with chest pain or pressure, fainting, severe dizziness, shortness of breath, confusion, heavy sweating, or collapse, treat that as urgent and seek emergency care rather than trying to wait it out. (health.clevelandclinic.org)

A “silent” arrhythmia can matter even when you barely feel it. For the most common sustained arrhythmia, this is well documented: "Due to its often-silent nature, detecting it can be challenging", and "Traditional detection methods often fail to identify paroxysmal or asymptomatic atrial fibrillation, leaving many patients undiagnosed until serious complications arise". In plain English: an arrhythmia can come and go, and symptoms can be a poor measuring stick. If you have repeated episodes, new palpitations with risk factors, or an irregular rhythm that keeps returning, the safest next step is to document it medically — not to guess from the sensation alone. Silent or subclinical AFib has been associated with adverse outcomes even when people do not feel symptoms, and reviews describe ECG, Holter, and other cardiac monitoring as the tools used to identify it. (pubmed.ncbi.nlm.nih.gov)

So yes, some arrhythmias can kill — especially rhythms that stop the heart from pumping, such as ventricular fibrillation, or unstable ventricular tachycardia. But most palpitations are not that. The useful middle ground is to take the pattern seriously without panicking: brief, rare flutters can often be discussed at a routine visit, while sustained, worsening, recurrent, or symptom-linked episodes need an ECG-based check. The goal is not to assign yourself a life expectancy number from the internet. It is to find out what rhythm you’re having, whether it changes your stroke or fainting risk, and what a clinician recommends to lower that risk.

What causes arrhythmias and palpitations

Palpitations are the feeling; an arrhythmia is one possible reason for that feeling. Your heart can race, thump, flutter, or “skip” when its electrical system is irritated, when your body is under strain, or when the heartbeat is normal but forceful enough for you to notice. Common short-term contributors include caffeine, alcohol, nicotine, stress or panic, dehydration, fever, poor sleep, and stimulant medications such as some cold medicines, asthma inhalers, ADHD medications, or recreational stimulants. Blood chemistry can matter, too: potassium, magnesium, calcium, and other electrolytes help heart cells fire in rhythm, so levels that are too low or too high can make beats feel jumpy or irregular. Palpitations can also come from thyroid problems — especially an overactive thyroid — anemia, infection, hormone shifts, structural heart disease, or a primary electrical rhythm problem. For a deeper cause-by-cause walkthrough, use the [arrhythmia causes guide](/arrhythmia/causes/) rather than trying to match yourself to a long checklist. (my.clevelandclinic.org)

Post-viral palpitations are also real enough to take seriously, especially if they are new for you, persistent, or paired with chest pain, fainting, unusual shortness of breath, or a major drop in exercise tolerance. After an infection, your nervous system, inflammation level, hydration, sleep, fever response, and heart muscle stress can all shift at once; sometimes that feels like a pounding or fast heartbeat even when no dangerous rhythm is found. After COVID-19 specifically, CDC lists a fast-beating or pounding heart — palpitations — among commonly reported Long COVID symptoms, and an American Heart Association scientific statement describes both arrhythmic and autonomic complications after COVID-19. (cdc.gov)

Research here is still evolving, so this is a reason to ask rather than a settled fact — but “it’s just anxiety” is not a good default when symptoms started after an illness. A systematic review set out to measure it — "This study aims to determine the long-term risk of developing cardiac arrhythmias after SARS-CoV-2 infection", noting that "even asymptomatic patients have evidence of cardiovascular injury after COVID-19". That does not mean every post-viral flutter is dangerous, and it does not mean you can diagnose an arrhythmia by feel. It means new, repeated, or worsening palpitations after infection deserve the same basic medical logic as any other rhythm concern: symptoms, risk factors, and an ECG or heart monitor if your clinician thinks it’s needed. (pmc.ncbi.nlm.nih.gov)

How arrhythmias are diagnosed

An arrhythmia is diagnosed by recording your heart’s electrical activity while the abnormal rhythm is actually happening. A clinician can suspect a rhythm problem from your story — a racing heart at night, skipped beats when lying down, dizziness, shortness of breath, chest pressure — but the diagnosis comes from a rhythm strip, not from the sensation itself.

The usual starting point is an ECG/EKG (electrocardiogram). It is quick, painless, and records the electrical signals that control your heartbeat at that moment. The catch is timing: if your palpitations come and go, a short in-office ECG can look normal simply because the episode stopped before the recording began. That does not mean you imagined it; it means the test did not catch the rhythm. (mayoclinic.org)

If symptoms are intermittent, clinicians use longer monitoring. A Holter monitor is a portable ECG device worn during normal life, often for 24–48 hours and sometimes longer, to look for rhythms a single ECG may miss. An event monitor or patch monitor can be worn for days to weeks — in some systems up to about 30 days — and you may press a button when symptoms happen, while some devices also auto-record suspicious rhythms. If episodes are rare, unexplained, or linked with fainting or stroke evaluation, an implantable loop recorder may be placed under the skin of the chest to monitor for much longer periods in select cases. (international.heart.org)

Consumer wearables sit in a different category. A smartwatch may flag an irregular rhythm, and some devices can record a single-lead ECG that you can share with a clinician. That can be useful information, especially when symptoms are brief and hard to catch. But a wearable alert is a screening prompt, not a final diagnosis: FDA materials for smartwatch irregular-rhythm notifications describe them as identifying rhythms suggestive of AFib and state that they are not intended to diagnose AFib or guide treatment; the 2023 ACC/AHA/ACCP/HRS atrial fibrillation guideline also notes that PPG-based irregular-rate algorithms are not reliable enough by themselves to establish an AF diagnosis. (accessdata.fda.gov)

So if your Apple Watch or another smartwatch flags possible AFib, or if you capture a single-lead ECG during palpitations, bring the recording and timing details to a healthcare professional. A clinician decides whether that tracing is diagnostic enough, whether you need a 12-lead ECG, Holter, patch, event monitor, or loop recorder, and what — if anything — should be done next. Treatment decisions should be based on a clinician-reviewed diagnostic recording, your symptoms, and your overall risk, not on a consumer alert alone. (heart.org)

This is also why longer or opportunistic screening is used in research and in higher-risk groups: rhythms like atrial fibrillation can be silent, brief, or easy to miss during a short appointment. Research context: "Guidelines recommend opportunistic atrial fibrillation (AF) screening in high-risk populations, including COPD patients". In that COPD outpatient-clinic study, a 14-day PPG-based pathway was used as a screening step, with cardiac work-up and ECG confirmation after concerning findings — a good example of the difference between “flagged for follow-up” and “diagnosed.” (pubmed.ncbi.nlm.nih.gov)

For deeper detail on what the ECG tracing shows and how Holter-style monitoring works, see the [ECG/EKG guide](/ekg-ecg/).

When to see a doctor / when to call 911

⚠️ Call 911 right away if a racing, pounding, fluttering, or irregular heartbeat comes with chest pain or pressure, fainting or nearly fainting, severe shortness of breath, confusion, or a heartbeat that suddenly feels extremely fast or extremely slow for you and makes you feel dizzy, breathless, or like something is seriously wrong. Those symptoms can mean your heart or brain is not getting enough blood or oxygen in the moment, so this is not a “wait and see” situation. The American Heart Association also advises calling 911 for chest pain or pressure, and for a heart rate that is suddenly very high or very low with symptoms such as chest pain, shortness of breath, dizziness, or fainting. (heart.org)

Also call 911 for possible stroke symptoms, even if they fade. Use FAST: Face drooping, Arm weakness or drifting down, Speech that is slurred or strange, Time to call 911. The CDC also lists sudden trouble walking, vision changes, confusion, one-sided numbness or weakness, and a sudden severe headache as stroke warning signs. (cdc.gov)

See a doctor promptly — not necessarily through the ER — if you have a new, persistent, or recurring irregular pulse; a very fast pulse that keeps coming back; palpitations that last more than a few minutes, happen often, or continue for days; a very slow pulse with dizziness or weakness; or palpitations when you already have known heart disease. Palpitations are often not dangerous, but a change from your usual pattern deserves evaluation, especially when episodes are lasting minutes to hours or affecting your quality of life. (heart.org)

Ask your clinician whether you need an ECG/EKG, Holter monitor, or event monitor. An irregular pulse you can feel — or a rhythm alert from a watch or other device — is a reason to get the rhythm documented medically, not a reason to self-diagnose. Arrhythmias are confirmed by recording the heart’s electrical activity, and the right test depends on how often the symptoms happen. (heart.org)

How to bring this up with your doctor — and what to ask for

Bring a log, not an adjective. "My heart races sometimes" is hard to act on; a short written record is not. For each episode note the date and time, what you were doing in the minute before it started, how it began and ended (gradually, or like a switch), how long it lasted, your pulse if you were able to take it, and what else you felt — dizziness, chest pain, breathlessness, faintness. Two weeks of that is more useful than a year of memory.

Ask for the rhythm to be recorded, not just described. A resting ECG only captures the rhythm during those ten seconds, so if your episodes come and go, ask directly whether you need longer monitoring — a Holter for a day or two, or an event or patch monitor for longer if episodes are less frequent. If you can capture an episode on a smartwatch ECG, bring that trace to the appointment.

Ask what should be ruled out before the episodes are labelled stress. Thyroid problems, anemia, electrolyte disturbances, fever, dehydration, some medications and stimulants can all drive palpitations, and they are found with basic tests rather than guesswork.

If you are brushed off and your symptoms continue, it is reasonable to say so plainly: the episodes are ongoing, I have written them down, and I would like a rhythm recording that covers one. Ask what would have to happen for a referral to cardiology to make sense, and what specifically you should watch for in the meantime. And whatever else is going on, treat fainting, chest pain, severe breathlessness, or a racing heart that will not settle as reasons for emergency care rather than a future appointment.

How Welltory fits

Welltory can help you notice patterns, but it is not a medical device and does not detect, diagnose, or rule out arrhythmias or palpitations. It measures heart rate and heart rate variability optically with PPG — using light-based pulse signals from your phone camera or a wearable — so what you see is a window into how your pulse and body state change with activity, rest, sleep, stress, and recovery, not an ECG tracing of the heart’s electrical rhythm. PPG can be useful for flagging irregular pulse patterns, but clinical guidance is clear that PPG-based signals are not reliable enough to establish an atrial fibrillation diagnosis; an initial diagnosis should be made by a clinician reviewing electrocardiographic signals. (pmc.ncbi.nlm.nih.gov)

So if you notice an irregular, unusually fast, or unusually slow pulse — in Welltory, on a wearable, or simply because you feel your heart racing, fluttering, thumping, or skipping — treat it as a reason to talk with a clinician and ask whether you need an ECG, Holter monitor, event monitor, or another rhythm test. Those tools record the heart’s electrical activity, and clinicians can compare the rhythm data with your symptom diary to see what was happening when you felt the episode. (heart.org)

Where Welltory can help is with context. If your “heart racing at night” feeling tends to appear after poor sleep, late caffeine, alcohol, hard training, dehydration, emotional stress, or a run of low-recovery days, that pattern may be worth bringing to your appointment. It can make the conversation more concrete: this is when I felt it, this is what my heart rate looked like, this is what was happening around it. But the boundary matters: Welltory cannot confirm that a rhythm is harmless, and it cannot exclude a heart-rhythm disorder. Only appropriate medical evaluation can do that.

How we made it

Data. Welltory `persona_daily_panel`, snapshot of 2026-09-22: 4,145 users and 359,866 user-days, filtered to `wearable_quality_ok = True` and to days with at least 120 awake sedentary minutes.

What we measured. For each day we took the 90th percentile of heart rate during awake, sedentary minutes — the high end of your pulse while you were up but not moving. That is the closest thing in our data to the moment people describe as "my heart was racing and I wasn't doing anything." It is a photoplethysmography estimate from a wearable or phone camera, not an electrocardiogram.

Controls we ran before publishing this.

• Comorbidity stratification. The share of people crossing 100 bpm barely moves with the number of self-reported conditions: 46.6% with none, 45.6% with one, 49.4% with two, 54.2% with three or more. This is not a "sicker people" effect.

• Sex. 47.4% of women and 48.1% of men — no meaningful difference.

• Age. A clear inverse gradient: 72.2% at 18–25, 67.8% at 26–35, 61.6% at 36–45, 48.8% at 46–55, 44.6% at 56–65, 34.6% at 65+. Arrhythmia risk rises with age; this falls with it, which is the point.

• Sensitivity. Requiring more sedentary time per day changes little: 47.7% at ≥60 and ≥120 minutes, 46.8% at ≥240, 44.3% at ≥360.

Limits. Observational, self-tracked, and not a clinical population — we do not know who among these users has a diagnosed rhythm disorder, and we did not attempt to find out. Optical pulse readings can be thrown off by movement, cold hands, and poor sensor contact, and they cannot distinguish a fast normal rhythm from an abnormal one. Nothing here should be used to rule a rhythm problem in or out. All figures are reported as anonymized, aggregated data; no individual user is identifiable.

The article itself was drafted with AI tools, then edited and fact-checked by the Welltory team.

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