Heart rate when falling asleep

What happens to your heart rate when you fall asleep?

It comes down in steps rather than one smooth slope. In a 1999 sleep-laboratory study that followed six people through repeated sleep onsets on three nights each, heart rate fell at every transition into sleep, jumped after every brief arousal back towards waking, and returned to its sleeping level within about 12 beats. By stable stage 2 sleep, both heart rate and breathing rate were lower than when awake (Burgess, Kleiman and Trinder, 1999).

Under the steps is a change of driver. In a 2001 study of 14 healthy young adults over three nights, the nervous system’s balance in non-REM sleep moved away from the sympathetic branch, which speeds the heart, towards the parasympathetic branch, which slows it — mainly because parasympathetic activity rose. In REM sleep the balance looked much like wakefulness, and heart rate also drifted down across the night under the body clock’s influence, as well as with the stage of sleep (Trinder and colleagues, 2001).

So the night has a shape: the heart slows on the way in, reaches its lowest in deep sleep, and climbs back towards waking levels during REM (NINDS). What happens when you fall asleep follows the rest of the body down.

What is a normal heart rate during sleep?

There is no single number. For adults awake and at rest, the British Heart Foundation gives a normal range of usually 60 to 100 beats a minute, says some people sit outside it, and adds that what is normal differs with age, health and sex; a rate below 60 can be normal in very fit people such as athletes (British Heart Foundation).

Asleep, the same heart beats more slowly than its own waking resting rate, for the reasons above — so a night-time figure below your daytime range is expected rather than alarming on its own. What the British Heart Foundation flags is a rate that is consistently fast, slow or irregular, especially if you also feel faint or dizzy.

Normal is also personal. In a 2020 study of 92,457 American adults who wore Fitbit trackers between 2016 and 2018, the average daily resting heart rate was 65 beats a minute, but individuals’ own averages ranged from 40 to 109 — one person’s normal could differ from another’s by as much as 70 beats a minute — while each person’s own rate stayed fairly steady over time (Quer and colleagues, 2020).

What is “resting heart rate” at night?

A wearable’s “resting heart rate” may already be largely a sleeping number: in that study, Fitbit’s daily figure was calculated mainly during periods of sleep (Quer and colleagues, 2020). Compare yours with your own usual, not with someone else’s.

What is HRV during sleep?

Heart rate variability (HRV) is the variation in time from one beat to the next. A heart is not a metronome: the gaps between beats lengthen and shorten all the time, and some measures of that variation track the parasympathetic, slowing side of the nervous system (Laborde and colleagues, 2022).

During sleep it follows the stages. In the 2001 study, HRV measures moved towards parasympathetic dominance in non-REM sleep and back to something like wakefulness in REM (Trinder and colleagues, 2001). It is also strongly individual: a common measure, RMSSD, depends heavily on age, which is one reason someone else’s number tells you little about yours (Pietilä and colleagues, 2018).

How accurate is a wearable at night?

Better for heart rate than for HRV or sleep stages. In a 2022 laboratory comparison of six devices against ECG and a full sleep recording in 53 healthy adults over one night, the devices that sampled heart rate during sleep agreed closely with ECG on heart rate and less closely on HRV, while all six needed improvement at telling sleep stages apart (Miller, Sargent and Roach, 2022). The laboratory received research support from WHOOP, one of the makers tested, which had no part in the study.

Are sleep trackers accurate? goes further, and orthosomnia is what can happen when the numbers start keeping you up.

Why is my heart racing when I try to sleep?

Most often for ordinary reasons. The NHS describes palpitations as a heartbeat that has become more noticeable — racing, pounding, fluttering or irregular — and says they are common and not usually a sign of anything serious. Among the common causes it lists stress and anxiety, lack of sleep, strenuous exercise, some medicines, and alcohol, caffeine, nicotine and recreational drugs (NHS).

Worry

In Allison Harvey’s cognitive model of insomnia, worry about sleep and about the day to come triggers autonomic arousal along with distress, and the anxious state turns attention towards signs that sleep is not coming (Harvey, 2002). A pounding heart is exactly the kind of internal signal that model describes people watching for. Racing thoughts at night is about the mind’s half of this.

Caffeine

Caffeine is on the NHS’s list, and it lasts longer than most people think: a coffee after lunch is still partly in your system at bedtime (caffeine has a very long tail).

Alcohol

A nightcap keeps the heart faster in the first hours of sleep, not slower. In a 2018 study of 4,098 Finnish employees who wore chest-strap heart recorders in everyday life, heart rate in the first three hours of sleep was higher on nights after drinking than on the same person’s alcohol-free nights — by an average of 1.4 beats a minute after a little alcohol, 4.0 after a moderate amount and 8.7 after a lot — and the parasympathetic side of heart regulation was suppressed in step (Pietilä and colleagues, 2018). Two of its authors were employed by Firstbeat, the company whose recorders and analysis it used. Alcohol is a sedative, not a sleep aid covers the rest of the night.

A late, hard workout

Evening exercise is not the problem it is often made out to be: a 2019 review of 23 studies in healthy adults found that, overall, it did not harm sleep, with a possible exception for vigorous exercise ending within an hour of bedtime (Stutz, Eiholzer and Spengler, 2019).

Late, hard sessions do show up in the night’s heart rate. In a 2025 analysis of a year of data from 14,689 people wearing WHOOP straps, the later and harder the workout, the higher that night’s resting heart rate and the lower its HRV, while sessions that ended at least four hours before sleep were not linked with changes in sleep (Leota and colleagues, 2025). It is an observational study, so it shows an association rather than cause and effect, and two of its authors are affiliated with WHOOP.

A jolt on the way down

A noise, or anything else that half-wakes you on the way down, briefly speeds the heart. In the 1999 study, the rise after each brief arousal had settled within about a dozen beats (Burgess, Kleiman and Trinder, 1999).

The NHS’s list also includes the menopause, pregnancy, and conditions such as iron deficiency anaemia, an overactive thyroid or a heart rhythm problem — one reason a new pattern is worth a doctor’s view rather than a guess (NHS).

Can slow breathing calm a racing heart?

It can shift the balance towards the slowing side. A 2022 meta-analysis of 223 studies found that breathing slowly on purpose increased the parasympathetic part of HRV while people did it, straight after a single session, and after programmes of several sessions (Laborde and colleagues, 2022).

That is not the same as a trial at bedtime in people lying awake, and it is no substitute for medical advice when the heart is doing something new. 4-7-8 breathing looks at the best-known bedtime version.

When should you see a doctor about a racing heart at night?

The NHS’s advice on palpitations is plain:

• Call 999 or go to A&E if you have palpitations that do not go away, or palpitations with chest pain, shortness of breath, or feeling faint or fainting. If those symptoms have stopped, ask your GP surgery for an urgent appointment or call 111.
• See a GP if palpitations keep coming back or are happening more often, last longer than a few minutes, or you have a heart condition or a family history of heart problems.

Those are the UK’s numbers. Elsewhere, call your local emergency number — 112 across the European Union, 911 in the US and Canada — or go to an emergency department.

The British Heart Foundation adds that not every change in heart rate means something is wrong, and that a heart rate monitor can help track your health but cannot diagnose a condition (British Heart Foundation). A number on a watch is a reason to ask, not an answer.