If you’ve ever woken up in the middle of the night, lain awake for an hour or two, and felt a wave of frustration, you’re not alone. But what if that break in your sleep is not a disorder, but a biological remnant of a once-universal human pattern? Historians and sleep scientists have uncovered compelling evidence that for centuries, people across Europe and other regions routinely slept in two distinct blocks: a “first sleep” of a few hours, followed by an hour or more of quiet wakefulness, then a “second sleep” until dawn. This article will walk you through the historical documentation, the physiological mechanisms that may support biphasic rest, the sociocultural shifts that erased this pattern, and how to safely explore segmented sleep if you’re curious. We’ll also address common pitfalls and whether this pattern is right for you in a 24/7 world.
In the early 1990s, historian A. Roger Ekirch at Virginia Tech began digging through thousands of pre-industrial diaries, court records, medical textbooks, and literary works. He found that references to “first sleep” and “second sleep” were routine in England, France, and other parts of Europe from at least the Middle Ages through the 18th century. People did not consider a night of continuous slumber the norm. Instead, they went to bed around 9 or 10 p.m., slept for three to four hours, then woke up for one to three hours. During this wakeful interval, they prayed, read, chatted with spouses, had sex, or even visited neighbors.
Ekirch cites the word “watch” as a common term for this middle-of-the-night period. In Shakespeare’s plays and Chaucer’s Canterbury Tales, characters refer to the “first sleep” or the “second sleep” as casually as we speak of “nighttime.” Medical texts from the 16th century even advised when to take medicines based on which sleep segment you were in. For example, a 1595 French doctor recommended that the best time to conceive a child was during the period after the first sleep, when the body was rested and the mind clear.
The shift toward a single consolidated block of sleep began with the spread of affordable oil lamps, gas lighting, and eventually electric light. By the late 19th century, people could stay awake longer into the night, pushing bedtime later and reducing the natural interval during which segmented sleep occurred. The Industrial Revolution also demanded strict schedules, and by the 1920s, the “monolithic” eight-hour sleep block became the cultural standard. The second sleep faded from common memory so quickly that by the 1970s, most people had never heard of it.
While the historical evidence is strong, the physiological question remains: does the human body naturally incline toward biphasic sleep under the right conditions? Several experiments suggest yes. In the early 1990s, psychiatrist Thomas Wehr of the National Institute of Mental Health conducted a landmark study. He exposed subjects to a “short photoperiod” — 10 hours of darkness per night — for several weeks, mimicking winter’s long nights. After initially struggling, subjects began to adopt a two-part sleep pattern: they slept for about four hours, woke up for one to two hours, then slept again for another four hours.
During that wakeful interval, Wehr’s subjects reported feeling calm, meditative, and sometimes even euphoric. Blood tests showed elevated levels of prolactin — a hormone associated with relaxation and milk production — similar to levels seen during restful wakefulness in nursing mothers. The body also released more melatonin during the dark period, which may help explain the relaxed state. Notably, the subjects did not feel anxious or stressed; they simply enjoyed the quiet time.
Under typical modern lighting — with electric lights, screens, and late-night activities — the brain receives signals that it is still daytime. Melatonin production is suppressed, and the natural pressure for a biphasic pattern is overridden. However, some sleep researchers argue that the “segmented” pattern may still be latent in many people. When they wake up at 2 a.m. and cannot fall back asleep, they may actually be experiencing a healthy first-sleep/second-sleep interval, not insomnia.
Curious about trying segmented sleep? You’re not alone — many self-experimenters have jumped in without preparation and ended up sleep-deprived. Here are the most frequent errors:
If you’re intrigued by the historical pattern and want to test whether it suits you, proceed methodically. Start during a vacation or a period with low daytime demands, ideally a season with naturally long nights (like winter).
Choose a 10-hour “dark window” — for example, from 9 p.m. to 7 a.m. Dim all lights after sunset; use blackout curtains. Go to bed at the start of your dark window. For the first several nights, you might sleep straight through. As your body adjusts, you may naturally wake after three to five hours. During that break, stay in dim conditions. Keep a glass of water nearby. If you feel anxious, practice slow, deep breathing (inhale for four counts, exhale for six). When you feel sleepy again, return to bed. Track your total sleep time with a simple sleep diary — don’t rely on a wearable that assumes a single block is normal.
If after three weeks you are still unable to achieve at least seven hours of total sleep per night, or if your daytime functioning (mood, concentration, reaction time) declines, revert to a monophasic schedule. Some people may find that the “second sleep” causes more anxiety than it relieves, especially if they have a history of insomnia.
No sleep pattern is universally superior. The biphasic model has advocates who cite unique benefits, but also clear drawbacks in modern life.
Some adherents report that the wakeful gap becomes a time of creativity and deep relaxation. Because prolactin levels are elevated, the period can feel restorative even while awake. In communities where biphasic sleep remains common (e.g., among some hunter-gatherer groups like the !Kung San in southern Africa), researchers have observed lower rates of chronic stress and more social bonding during nighttime hours.
Social and occupational scheduling can become a major obstacle. If you have a partner who sleeps monophasically, your midnight waking may disturb them. Many jobs and social events extend past 10 p.m., making an early bedtime impractical. Furthermore, the lack of artificial lighting during the break can be challenging in winter, and modern homes are rarely designed for a two-hour gap in the middle of the night.
Labeling the single-block model as “unnatural” oversimplifies. While historical evidence confirms that biphasic rest was the norm for centuries, that does not mean it is inherently healthier. Contemporary sleep science consistently shows that for the majority of people, a consolidated 7–9 hour sleep is associated with better cardiovascular health, cognitive function, and emotional stability. The key is that the body is adaptable: given prolonged darkness and no scheduled demands, it often splits sleep. Given bright lights and fixed work hours, it consolidates. Neither pattern is “unnatural” — both are natural responses to different environments.
Genetics play a major role. Some people have a natural “short sleep” gene (DEC2 mutation) and thrive on less than six hours, but this is rare. Others have a “long sleep” gene and need nine or ten hours. Similarly, some individuals find biphasic sleep deeply calming, while others feel fragmented and irritable. There is no one-size-fits-all prescription.
Whether you choose monophasic or biphasic sleep, certain habits consistently improve rest quality. Prioritize consistent wake times (even on weekends) to anchor your circadian rhythm. Keep your bedroom cool (around 65°F) and pitch-black. Limit caffeine after 2 p.m., and avoid alcohol in the three hours before bed — alcohol initially helps you fall asleep but fragments the latter half of the night, which can mimic the wakeful gap you might otherwise enjoy.
If you do wake up at 2 a.m. and feel alert, do not force yourself to stay in bed. Getting up for 20–30 minutes in dim light, doing a quiet activity, and then returning to bed often resolves the issue more effectively than tossing and turning. Recognize that a brief nocturnal awakening is not necessarily a problem — it may be a normal rhythm waiting to be met with acceptance rather than frustration.
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