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Biphasic sleep is a sleep pattern that consists of sleeping in two sessions during a 24-hour period. It may also be called bimodal, segmented, or divided sleep. So, it refers to sleeping habits that involve a person resting in two segments per day. If you sleep half the night, get up for an hour or two, and return back to bed, you are a biphasic sleeper. Other examples of segmented sleep may involve sleeping during the night and taking a midday nap. If you are a bimodal sleeper, don’t worry, you are not alone. Although most people are monophasic sleepers, biphasic sleep pattern is historically common and biologically natural.

Types of Sleep Patterns

Before we take a look at the history of bimodal sleep, we should learn what kind of sleep patterns exist, and how they affect a person’s health and sleep hygiene. An individual’s sleep pattern is dependent on their internal circadian rhythm. Thanks to their inner clock, all human beings have a routine of biological and behavioral processes that occur every day over a 24-hour period. There are three main types of sleep patterns – monophasic, biphasic and polyphasic sleep.

Monophasic sleep is what modern society would refer to as a normal sleep pattern. This sleep pattern became the norm during the industrial revolution and was most likely caused by increasing hours of working time (more on this later).

Biphasic sleep pattern involves sleeping in two segments for 5 or 6 hours per night and having a shorter or a longer pause in between.

Polyphasic sleep consists of shortly resting multiple times during the day. There are three combinations of polyphasic sleeping – the everyman, the uberman, and the dymaxion.

  • Everyman sleeps around 3 hours and takes around three 20-minute naps during the day.
  • Uberman sleeps 3 hours a day, but only in the form of six 30 minute naps.
  • Dymaxion sleeps only 2 hours a day, in the form of 30-minute naps every 6 hours.

History of Biphasic Sleeping

Thanks to the research conducted by a historian Roger Ekirch, a professor of Virginia Tech, we know how people used to sleep in the past. The seminal paper that took him 16 years of research revealed that people didn’t have eight hours of uninterrupted sleep as we do today, but actually slept in two distinct segments. Ekirch believes that people embraced a biphasic sleep pattern until electric light became common. People would go to bed at dusk, then spent a few hours awake around midnight and finally returned to sleep for the rest of the night.

Roger Ekirch’s book titled “At Day’s Close: Night in Times Past”, published in 2005, contains more than 500 references to segmented sleeping patterns, starting from diaries and medical books, to Homer’s Odyssey and other famous literary works. For example, in literature from the Renaissance era – The Canterbury Tales, from the 14th century, one character says she will return to bed after her first sleep.

The references in Ekirch’s book describe a segmented sleeping pattern that involves sleeping two times a day. These periods are called first and second sleep. The first sleep starts around two hours after dusk and lasts for approximately four hours. After these four hours, the person would wake up and stay awake for one or two hours, engaging in different activities. After that, the person would go back to bed and fall into a second sleep. You may be wondering what were people doing between their first and second sleep. According to Roger Ekirch’s work, people use that time to read, write, pray, have sex, smoke or to simply hang out with friends. An interesting fact is that prayer manuals from the 15th century had special prayers for the hours between first and second sleep. In the late 17th century, mentions about segmented sleep slowly started to disappear, and the idea completely receded until the 1920s.

The reason for this is probably an improvement in street lighting and domestic lighting. A sudden surge in coffee houses has also influenced biphasic sleep patterns. Due to electricity and improved street and domestic lighting, then night finally became a place for legitimate activities, and as those activities increased, the amount of time people had for resting decreased. Some research suggests that when humans use only natural light, they may fall into a bi-modal sleep pattern.

During the period of the industrial revolution, our sleep patterns and habits also had to undergo some changes. People because more time-conscious and sensitive to efficiency, which further decreased total sleep time. During the industrial revolution, we can come across some medical journals that report parents had to force their children out of a biphasic sleep pattern. This was done by not allowing the children to have a second sleep one they woke up naturally from the first one. Kids were allowed to have a second sleep only if they were sick.

Today, we have all adapted to monophasic sleep pattern or eight-hour sleep, and we can definitely say that the modern industrial workday shaped this type of sleep pattern, or the custom to sleep 6 to 8 hours per day. Apart from monophasic sleep, biphasic and even polyphasic sleep patterns manifest naturally in some people.

Although monophasic sleep pattern is the most common one, some people still prefer and practice bi-modal sleep. For example, some orders of monks and nuns wake in the middle of the night to pray. These prayers are known as Matins. Since they break up their night, the practitioners are basically forced to create a biphasic sleep pattern. Some Muslims follow a similar pattern – they wake in the middle of the night to pray and then go back to sleep until morning. Research shows that people who follow these practices sleep healthy and that their sleep cycle is normal during both sleep periods.

It is interesting to mention that Ekirch believes some sleeping problems people experience at night, such as sleep maintenance insomnia or inability to stay asleep during the night, may be a natural occurrence that derives from biphasic or segmented sleep. When we have troubles to stay asleep at night, we may feel anxious, which will further prevent peaceful snoozing — however, scientists like dr. Russell Foster from Oxford University says that waking up in the middle of the night occasionally is completely normal and actually presents a throwback to the bi-modal sleep pattern.

A behavioral sleep medicine specialist, Gregg Jacob, believes people in the past were forced into periods of rest and relaxation between first and second sleep in order to reduce their stress levels in a natural way. Nowadays, although this may be good for us, we simply don’t have enough time for it. Some scientists believe bi-modal sleep is healthier for people who experience a lot of stress on a daily basis or suffer from anxiety and depression.

How Common is Biphasic Sleep?

Although Ekirch said in his book that bi-modal sleep disappeared until the 1920s, research shows that even up to 60% of adults may have two distinct sleep patterns per night or biphasic-type sleep cycles.

Is Biphasic Sleep Harmful?

Biphasic sleep isn’t harmful to your health. Many people with a bimodal sleep pattern get enough rest and wake up refreshed in the morning without experiencing daytime fatigue or other symptoms of sleep deprivation. However, midnight awakenings may cause anxiety and increase one’s stress levels if they believe they have insomnia. Sometimes, it’s very hard to differentiate insomnia from bi-modal sleep patterns. Without proper diagnosis, biphasic sleep patterns may be mistaken with false insomnia or precisely speaking – sleep maintenance insomnia or inability to stay asleep.

Biphasic vs. Polyphasic Sleep

The terms such as divided or segmented sleep can also refer to polyphasic sleep. While biphasic sleep describes a bimodal sleep pattern, polyphasic is a pattern with more than two sleeping periods in 24 hours. Many people decide to pursue a bimodal or polyphasic sleep lifestyle because they think it creates more time for them to complete tasks, enjoy certain activities, and simply be more productive. However, you can enjoy the same benefits of sleeping with monophasic and polyphasic sleep patterns.

In rare cases, people follow biphasic or polyphasic sleep schedules naturally. It’s much more common that polyphasic sleep pattern appears as a result of a sleep disorder or disability. For example, the irregular sleep-wake syndrome is one example of polyphasic sleep. Those who suffer from this condition tend to go to sleep and wake up at scattered and irregular intervals. They rarely feel well-rested and refreshed in the morning. Most of the times, they are fatigued and drowsy.

Types of Biphasic Sleep

In the past, people practiced biphasic sleep by sleeping in two segments during the night. However, there are other ways people can have a biphasic sleeping schedule. For example, by taking afternoon naps, also known as “siestas”, you are practicing bimodal sleep. It’s an interesting fact that siestas are a cultural norm in European countries such as Spain and Greece.

Taking naps also counts. You can either take a short 20-minute nap if you are typically sleeping around 6 hours per night, or you can sleep around 5 hours per night and take long one hour naps in the middle of the day. We did some research online, and many people actually report that biphasic sleep patterns really work for them, as well as that taking naps and splitting their sleep schedules helps them feel more alert during the day.

What Does Science Have to Say?

Many people report biphasic sleep positively influences their performance; however, research on whether there are indeed health benefits of bimodal sleep is mixed. A study carried out in 2016 on segmented sleep patterns argues that biphasic and polyphasic sleep patterns weren’t unusual before the industrial era. As mentioned in the beginning, scientists believe we developed a monophasic 8-hour sleep pattern due to the rise of the modern workday and artificial illumination technology.

We are all aware of the benefits of napping – short power naps that last 15 to 20 minutes were associated with better cognitive function and performance. However, other studies suggest that napping isn’t recommended for rest or cognitive development, especially if it affects sleeping during the night. In adults, napping can even be associated with increased risk of sleep deprivation.

Polyphasic sleep is not recommended because it’s doesn’t give you adequate time to go through all sleep stages and properly restore your body and mind. Sleep deprivation, apart from affecting your daily performance in multiple aspects, also increase the risk of severe health conditions, such as obesity, heart disease, and diabetes.

Biphasic sleep schedules are significantly less harmful than polyphasic sleep. Science, as well as historical and ancestral records on sleeping patterns, shows that bimodal sleep may be beneficial for human beings, and even improve their wakefulness, alertness, and cognitive function. However, other research shows that those are only temporary effects that occur due to raised stress hormones in the body, cortisol, and adrenaline.

It may not be a bad idea to try segmented sleep when you are working on an important project and need to squeeze more wake hours into your day. But changing your sleep patterns simply for the sake of change is not recommended and definitely not worth the increased health risks that could arise due to sleep deprivation.

Another disadvantage of bimodal sleep-wake cycle is that your wakefulness may not be compatible with your social life. This can negatively affect your personal and work relationships. On the flip side, this sleep pattern may be just ideal for shift workers or parents who need a quick boost of energy when taking care of their children.

Don’t forget that we are creatures of routine and that changing sleep patterns can be very difficult. If your transition to segmented sleep is unsuccessful, your body will be severely affected. Disrupting sleep patterns may harm your cells, tissues, and organs, and increase the risk of obesity and heart problems. Keep in mind that biphasic sleep schedules may not work for everyone and that they may be harmful when practiced long-term. There is nothing that can replace a good night of 8-hour restorative sleep.

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