Fast Fact:
Biphasic Sleep
Biphasic Sleep: Did Humans Really Sleep in Two Shifts? The Lost History of Biphasic Sleep
Have you ever woken up in the middle of the night, looked at the clock, and thought, "Why can't I just sleep through the night?" Modern sleep advice often suggests that uninterrupted sleep is the hallmark of healthy rest. But historians and sleep researchers have uncovered evidence that, for much of human history, waking during the night may have been completely normal. For centuries, many people practiced biphasic sleep—a pattern of sleeping in two separate periods with a period of wakefulness in between. Rather than lying awake frustrated, they expected it.
What Is Biphasic Sleep?
Biphasic sleep simply means sleeping in two distinct periods within a 24-hour day. Today, this often refers to sleeping at night and taking an afternoon nap. Historically, however, biphasic sleep usually meant something different: People went to bed shortly after sunset, slept for about three or four hours, woke naturally for one to three hours, and then returned to bed for a "second sleep" until dawn. Historical documents referred to these periods as "first sleep" and "second sleep," suggesting that this schedule was so common that it required no explanation.
Rediscovering a Forgotten Sleep Pattern
The modern interest in biphasic sleep began with historian Roger Ekirch, who spent years examining diaries, court records, medical texts, literature, and personal letters dating back hundreds of years. To his surprise, he found hundreds of references to "first sleep" and "second sleep" across Europe and beyond. These weren't descriptions of unusual behavior—they were written as though everyone understood exactly what they meant. People commonly used the quiet hours between sleeps to:
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Pray or meditate
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Read by candlelight
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Talk with family members
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Tend the fire
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Complete household chores
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Write letters
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Even visit neighbors
For them, being awake in the middle of the night wasn't considered insomnia—it was simply part of a normal night's rest.
Why Did People Sleep This Way?
The answer may lie in the world before electricity. Without artificial lighting, evenings were much darker. People often became sleepy soon after sunset and went to bed earlier than most people do today. After several hours of sleep, they would awaken naturally during the middle of the night. Following a period of quiet activity, they returned to bed for another few hours before sunrise. This schedule fit well with seasonal changes, agricultural life, and the natural cycle of daylight and darkness.
Is Biphasic Sleep Natural?
Possibly. One intriguing study conducted by psychiatrist Thomas Wehr at the National Institute of Mental Health explored what happens when modern people are exposed to long periods of darkness. Participants lived for several weeks with approximately 14 hours of darkness each day, similar to winter conditions before electric lighting. After an adjustment period, many participants spontaneously adopted a sleep pattern remarkably similar to historical accounts. They slept for about four hours, woke for one to three hours in a calm, relaxed state, and then fell asleep for another four hours. The findings suggested that segmented sleep may emerge naturally under certain lighting conditions, although this does not necessarily mean it is the "correct" or universal human sleep pattern.
What Happened to Biphasic Sleep?
The shift toward sleeping in one continuous block appears to have occurred gradually. Several cultural changes contributed:
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Artificial lighting allowed people to stay awake later.
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Urbanization changed daily routines.
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The Industrial Revolution emphasized fixed work schedules.
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Schools and factories rewarded uninterrupted nighttime sleep.
As bedtime moved later while wake-up times remained fixed, the period between first and second sleep gradually disappeared.
Eventually, sleeping in one continuous block—known as monophasic sleep—became the cultural norm in many industrialized societies.
Image idea: A simple historical timeline visual showing:
Pre-electricity → First Sleep → Wakefulness → Second Sleep → Industrial Revolution → Modern Monophasic Sleep.
Use warm historical imagery transitioning into a modern city/nighttime environment.
Does Waking Up at Night Mean You Have Insomnia?
Not necessarily. Many people briefly awaken several times during the night without remembering it. Others wake for longer periods and immediately become anxious because they believe something is wrong. Knowing that our ancestors commonly experienced a period of wakefulness can sometimes help reduce that anxiety. However, regularly waking during the night with distress, difficulty falling back asleep, or daytime fatigue may still indicate insomnia or another sleep disorder and should be discussed with a healthcare professional. In other words, waking at night is not automatically a sign that your sleep is unhealthy.
Should You Try Biphasic Sleep?
For most adults, major sleep organizations continue to recommend 7–9 hours of total sleep each night, regardless of whether that sleep occurs in one block or, in some cases, is supplemented with a short daytime nap. There is no strong evidence that historical segmented sleep is inherently healthier than consolidated nighttime sleep for people living modern lifestyles. The "best" sleep schedule is one that provides enough high-quality sleep to support your health, mood, and daily functioning.
The Bottom Line
For centuries, millions of people may have slept in two separate shifts each night. Historical records describe a world where waking for an hour or two after "first sleep" was an ordinary part of life rather than a reason for concern. Although modern society has largely abandoned this pattern, research suggests that segmented sleep may reflect one of the many ways the human brain can organize sleep under different environmental conditions. So if you occasionally wake in the middle of the night, remember: your brain may simply be following a rhythm that was once perfectly ordinary.
Learn More
BBC Future: The Forgotten Medieval Habit of "Two Sleeps" by Zaria Gorvett
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Roger Ekirch (2005). At Day's Close: Night in Times Past. A landmark historical examination of nighttime life and the evidence for segmented sleep.
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Wehr, T. A. (1992). "In Short Photoperiods, Human Sleep Is Biphasic." Journal of Sleep Research. This classic experiment examined how extended periods of darkness affected human sleep patterns and found that participants often adopted a two-part sleep schedule under those conditions.