Biphasic sleep means sleeping in two blocks per 24 hours instead of one. It comes in two forms: a long night’s sleep plus a daytime nap, or a night split in two with an awake period in between, called segmented sleep. Historical records and one lab study suggest people once slept in two segments, but field studies of non-industrial groups disagree, so it is not proven to be the one natural way. Short naps under about 30 minutes appear low risk, while long habitual naps are linked to worse health in observational studies. Either form needs the same total sleep: seven or more hours. Waking briefly at night can be normal and is not always insomnia. This is educational information, not medical advice.
From the practice
[RILEY: Add 2–3 sentences from your own client work. For example, what clients tell you when they wake in the night and worry that something is wrong, or how often a short nap helps or hurts their night sleep. Only include what you have actually observed. Delete this block if you’d rather not include it.]
What is biphasic sleep?
Biphasic sleep means sleeping in two separate blocks across a 24-hour day instead of one. The word covers two quite different patterns, and mixing them up causes a lot of confusion online.
- Monophasic sleep: one long block, usually at night. This is the modern default.
- Biphasic sleep with a nap: one main night sleep plus a daytime nap, often called a siesta.
- Biphasic sleep, segmented: a night split into a “first sleep” and a “second sleep,” with about one to three hours awake in between.
- Polyphasic sleep: three or more sleep blocks a day. A National Sleep Foundation panel found no evidence that it helps (see below).
The nap type and the segmented type have very different evidence behind them, so this guide treats them separately.
Did people really sleep in two blocks before electric light?
In some places and times, yes. But it is not proven to be the single natural human pattern.
Historian Roger Ekirch combed through documents spanning two thousand years. He found repeated references to a “first sleep” and a “second sleep” in English, Italian, French, and Latin, with both phases lasting about the same time. People used the gap for prayer, chores, conversation, and more. The references began fading in the late 1600s.
A lab study agrees. In the early 1990s, psychiatrist Thomas Wehr kept volunteers in 14 hours of darkness a night for a month. After a few days of long sleep to repay debt, they settled into about four hours of sleep, one to three hours awake, and about four more hours of sleep. The second sleep was lighter, with more REM and less deep sleep.
The field evidence is split. A 2017 study in a rural Madagascar village without electricity found a peak in activity after midnight on 49% of nights, consistent with segmented sleep. But a 2015 study of three foraging groups in Tanzania, Namibia, and Bolivia found one long bout of sleep and no segmentation. A 2017 study of the Hadza hunter-gatherers found short, flexible sleep, about 6.25 hours, with an early-morning sleep period and opportunistic daytime napping.
The fair takeaway is that human sleep appears flexible. Two blocks can be natural under some conditions, and one block under others.
Is biphasic sleep healthy?
It depends on which type you mean, and on whether you still get enough total sleep. The American Academy of Sleep Medicine and the Sleep Research Society say adults need seven or more hours per 24 hours. Splitting your sleep does not change that number.
Biphasic sleep with a nap
The evidence is mixed and mostly observational. A 2007 Greek study of more than 23,000 adults found that people who napped regularly had about 37% lower coronary mortality. But a 2024 review of 44 cohort studies, covering about 1.86 million people, found that habitual napping was linked to a higher risk of death, heart disease, metabolic disease, and cancer, and a lower risk of cognitive impairment and sarcopenia. Naps of 30 minutes or longer carried higher risks, while naps under 30 minutes showed no significant risk.
These studies cannot prove cause and effect. People may nap more because of poor night sleep or an underlying illness, so a nap can be a marker rather than the cause. Our complete guide to napping covers how to nap without wrecking your night.
Segmented sleep (first sleep and second sleep)
There are no good trials of deliberately splitting the night in healthy people. History and Wehr’s study suggest it can be natural when nights are very long, but nobody knows whether choosing it improves health or performance. Some sleep experts have noted that waking between two sleeps may be normal rather than a disorder, which could change how we think about night waking.
Do you wake at night and can’t tell whether it’s normal or a problem? If it’s wearing you down, book a consultation and we’ll look for the root cause.
Is waking up in the middle of the night normal?
Sometimes, yes. Brief waking can be part of normal sleep, and specialists have noted that waking between two sleeps may reflect an older natural pattern. It becomes a problem when it is frequent, distressing, or hurts your days.
Chronic insomnia disorder is diagnosed when symptoms happen at least three nights a week for at least three months, cause distress or impairment, and are not explained by another condition.
If you wake and cannot go back to sleep, keep the lights low and avoid checking your phone. If you have been awake a while, get up and do something calm until you feel sleepy. That is stimulus control, a core CBT-I tool. For more tactics, read how to go back to sleep after waking at night. If you wake around 2 or 3 a.m., see why you wake up at 3 a.m.
Who might try biphasic sleep, and who should skip it?
It may suit you if you already feel better after a short early-afternoon nap and still sleep well at night, or your schedule allows a midday break. Short naps under 60 minutes showed the best cognitive benefits in a recent umbrella review.
Be careful or skip it if:
- You have insomnia. Daytime naps can make night sleep harder for some people.
- You nap for an hour or more most days. That pattern was linked to a 30% higher risk of coronary heart disease in an umbrella review.
- You want to use a split schedule to get less total sleep. There is no reliable evidence that a biphasic schedule lets you need less. See natural short sleepers.
- You feel very sleepy every day despite seven to nine hours in bed. A sleep disorder such as sleep apnea may be involved.
How can you try biphasic sleep safely?
- Protect total sleep. Aim for seven or more hours across 24 hours.
- Keep naps short and earlier in the afternoon. Thirty minutes or less is the range with no significant added risk in one large review. Earlier naps are less likely to eat into your night sleep drive.
- If you wake at night anyway, stay calm, keep lights low, and avoid work or screens. Pick a point at which you will get up if sleep does not return.
- Track for two weeks. Note night sleep, naps, daytime energy, and mood.
- Stop and check in if night sleep gets worse or daytime sleepiness grows.
For how sleep stages shift across the night, see our guide to sleep cycles and stages.
What the Research Shows
Historical records show two sleeps. Ekirch’s archival work, covering documents across about two thousand years, found references to a first sleep and a second sleep in several European languages, with the two phases lasting about the same time. Household accounts describe going to bed a couple of hours after dusk, waking a few hours later for one to two hours, then sleeping until dawn. References faded from the late seventeenth century.
A lab study reproduced the pattern. In Wehr’s 1992 experiment, volunteers lived in 14 hours of darkness a day for a month. Their sleep became biphasic, split into two bouts several hours long with a one-to-three-hour waking interval between them. The second bout contained more REM and less deep sleep. Short-photoperiod laboratory conditions are extreme, though, and this does not show that everyone should split their night.
Field studies disagree. A 2017 study in Madagascar reported segmented sleep, with an activity peak after midnight on 49% of nights. A 2015 Current Biology study of three foraging societies found one long sleep bout and no evidence of segmentation. A 2017 Hadza study reported flexible sleep with a consistent early-morning period plus daytime napping, an average of 6.25 hours of sleep, and a sleep efficiency of 68.9%. The authors proposed that flexibility in sleep timing has itself been shaped by evolution.
Nap research gives mixed signals. The 2007 Greek cohort of more than 23,000 people linked regular napping to lower coronary mortality. A 2024 review of 44 cohort studies found higher risks of death, cardiovascular disease, and metabolic disease with habitual napping, especially for naps of 30 minutes or longer, but lower risks of cognitive impairment. A 2026 umbrella review of 16 meta-analyses found that naps under 60 minutes maximized cognitive benefits, while naps over 60 minutes were linked to a 30% higher risk of coronary heart disease. All of this is observational.
This article is for education only and is not medical advice. Talk with a qualified clinician about your own sleep, health conditions, and medications.
If you would like to see how we might be able to help you with this deeper, schedule a free consult here.
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When to Seek Professional Help
- You wake in the night often, feel distressed about it, or your days suffer. If it happens at least three nights a week for several months, ask about insomnia treatment such as CBT-I.
- You need long naps most days, or you feel very sleepy despite seven to nine hours in bed. A sleep disorder may be involved.
- You snore loudly, gasp or choke at night, or wake with headaches. These can signal sleep apnea.
- You are averaging under seven hours total and using a split schedule to cope.
- You feel persistently sad or hopeless, or have thoughts of self-harm. Contact a clinician right away, and in the US you can call or text 988 at any time.
Frequently Asked Questions
What is biphasic sleep?
Biphasic sleep means sleeping in two separate blocks across 24 hours instead of one. It takes two forms. One is a long night’s sleep plus a daytime nap, often called a siesta. The other is segmented sleep, in which the night is split into a first sleep and a second sleep with a waking period of about one to three hours in between. Both forms still need roughly seven or more hours of total sleep for most adults.
Is biphasic sleep healthy?
It depends on the form and on total sleep. Short naps under about 30 minutes showed no significant risk in one large review of cohort studies, while habitual naps of 30 minutes or longer were linked to higher risks of death and heart and metabolic disease. These studies are observational, so they cannot prove cause. For segmented sleep, there are no good trials of deliberately splitting the night, so its health effects are unknown. Adults still need seven or more hours total.
What is the difference between biphasic and polyphasic sleep?
Biphasic sleep uses two sleep blocks a day, while polyphasic sleep uses three or more, often with very short sleeps. A 2021 National Sleep Foundation panel found no evidence of benefits from polyphasic schedules and linked them, and the sleep loss they cause, to worse physical health, mental health, and performance. Biphasic patterns that still provide enough total sleep are far less extreme, but they are not proven to be better than one block.
Is it normal to wake up in the middle of the night?
Waking briefly during the night can be normal, and it is not always insomnia. Some sleep experts note that waking between two sleep periods may reflect an older natural pattern. It becomes a problem when it causes distress or daytime trouble. Chronic insomnia disorder is diagnosed when symptoms happen at least three nights a week for at least three months. If you wake often and feel unrested, track your nights and ask a clinician about causes like sleep apnea or stress.
Did humans really sleep in two shifts?
Probably in some places, but not everywhere. Historian Roger Ekirch found references to first sleep and second sleep in diaries, court records, and literature across about two thousand years of European history. A lab study with 14-hour nights produced two sleep blocks, and a Madagascar village showed segmented sleep on about half of nights. Yet a study of three foraging groups in Tanzania, Namibia, and Bolivia found one long sleep bout, so the question is still open.
When to Work With a Sleep Consultant
If you wake at night, nap to cope, or have tried different sleep schedules without lasting results, a deeper cause may be involved: your circadian rhythm, nervous system, hormones, gut, or nutrient status. The Sleep Consultant looks for those root causes instead of handing you generic sleep-hygiene tips.
