Daytime Naps: Why You Sleep Twice Daily

Sleep is an essential part of our lives, and for most people, it happens in one go. However, some people sleep twice a day, and this is known as biphasic sleep. This sleep pattern involves two sessions in a 24-hour period and can take various forms. For instance, some people sleep for a few hours at night, wake up for a couple of hours, and then sleep for a few more hours. Others sleep for a longer stretch at night and take a short nap during the day. While biphasic sleep may offer benefits such as improved alertness and productivity, it may not be suitable for everyone due to work or social commitments. Additionally, there is limited research on its long-term effects, and it may not be enough to meet the recommended sleep duration for adults.

Biphasic sleep involves two sleep periods in a 24-hour period

Biphasic sleep can take two forms. The first is where a person sleeps for a few hours at night, wakes up for a couple of hours, and then sleeps for several more hours until dawn. The second form is where a person sleeps for several hours at night and then takes a short nap during the day. In both cases, a person practising biphasic sleep should still obtain a total of at least seven hours of sleep per 24-hour period.

The idea of biphasic sleep is not new. In pre-industrial times, it was normal for people to get up for a couple of hours in the middle of the night. People spent this time praying, smoking, having sex, or even visiting their neighbours. Historical references to this cultural sleeping pattern can be found in art, diaries, literature, and medical texts. Historical figures including Plutarch, Virgil, Homer, and Chaucer all referred to the concept of first and second sleep.

Some people still adopt biphasic sleep patterns in contemporary settings to reduce the effects of lost sleep and maintain productivity. It is also practised in several parts of the world, such as Spain, Italy, and Greece, in the form of the "siesta".

Monophasic sleep is one extended sleep session, usually at night

Monophasic sleep is a sleep pattern where a person sleeps in one block of time, typically during the night. This is the most common sleep pattern in modern society, with most people sleeping for one 6-8 hour segment per day.

The custom of sleeping for one extended period at night may have been influenced by the modern industrial workday. During the industrial era, artificial lighting enabled people to stay awake past sunset, and the longer work hours meant that people slept for fewer hours at night.

However, monophasic sleep may not be the healthiest option for everyone. Some people may find that they feel more rested and alert with biphasic or polyphasic sleep patterns.

Additionally, exposure to artificial light at night can decrease melatonin levels and negatively impact sleep. Therefore, some people may benefit from limiting their exposure to artificial light before bedtime and adopting good sleep hygiene practices.

Polyphasic sleep is sleeping more than twice per day

Polyphasic sleep is not the norm for most humans, who usually engage in monophasic sleep, or sleep in one large block of time each day. Polyphasic sleep is common in many animals and is believed to be the ancestral sleep state for mammals.

There are three popular polyphasic sleep schedules: the Uberman Sleep Schedule, the Everyman Sleep Schedule, and the Triphasic Sleep Schedule. The Uberman Sleep Schedule involves six 20-minute naps spaced evenly throughout the day, totalling two hours of sleep per 24-hour period. The Everyman Sleep Schedule includes sleeping for three hours during the night and supplementing with three 20-minute naps throughout the day, for a total of four hours of sleep each 24-hour period. The Triphasic Sleep Schedule involves three short sleep periods after dusk, before dawn, and in the afternoon, providing a total of four to five hours of sleep per 24-hour period.

Polyphasic sleep schedules are not for everyone and may cause sleep deprivation. There is little scientific evidence to support the claims that polyphasic sleep schedules are inherently safe or provide benefits such as improved mental clarity and productivity. In fact, there are serious dangers associated with short and long-term sleep deprivation, as well as circadian rhythm misalignment. These include an increased risk of impaired immune function, mental health conditions, certain cancers, and even death in certain individuals.

Some people intentionally adopt a polyphasic sleep schedule in hopes of becoming more productive. However, for most people, following a polyphasic sleep schedule—particularly one that reduces total sleep time—leads to sleep deprivation and its associated negative physical and mental health outcomes.

Siesta sleep is a biphasic sleep pattern common in Spain and Greece

Siesta sleep is a biphasic sleep pattern that is common in Spain and Greece. Biphasic sleep involves two sleep periods: a longer night of sleep and a shorter daytime nap. This type of sleep pattern is also known as bimodal, diphasic, segmented, or divided sleep.

Siesta sleep usually consists of a long core sleep at night and a shorter core sleep during the day. The daytime core typically occurs during the circadian dip in the early afternoon and often includes a full sleep cycle, which is more restorative than a short nap. The longer daytime sleep also allows for a shorter night of sleep. The period of wakefulness between the two cores can be between 6-9 hours.

Siesta sleep is a very common sleep pattern in Spain and has also been adopted in many other countries around the world. It is often practiced by athletes who perform intense exercises, as the daytime core provides recovery after a workout session and grants extra sleep time to meet the increased slow-wave sleep (SWS) requirement.

In Greece, a study found that 43% of adolescents reported taking a siesta regularly, and 46% reported taking one occasionally. The median duration of the siesta was 1.5 hours.

Segmented sleep is sleeping in two or more shifts

Segmented sleep, also known as biphasic sleep, involves sleeping in two shifts or segments per day. This can take the form of a longer nighttime sleep and a shorter daytime nap, or two nighttime sleep sessions with a couple of waking hours in between.

The idea of segmented sleep is not new. In pre-industrial times, it was normal to wake up for a couple of hours in the middle of the night. People would spend this time praying, smoking, having sex, or visiting their neighbours. This was also the case for much of human history, as referenced in historical art, diaries, literature, and medical texts. Historical figures such as Plutarch, Virgil, Homer, and Chaucer all referred to the concept of "first sleep" and "second sleep".

Some people still adopt segmented sleep in contemporary settings to reduce the effects of lost sleep and maintain productivity. It is also a common sleep pattern in many European cultures, such as in Spain and Greece, where it is known as "siesta sleep".

There are potential benefits to segmented sleep, including improved cognitive function, productivity, and stress reduction. It can also increase flexibility in scheduling and improve dream recall. However, there is limited research on the long-term effects of segmented sleep, and it may not be feasible for those with strict work schedules or family commitments.

If you are interested in trying segmented sleep, it is recommended to choose a sleep pattern that suits your personal preferences and goals, limit your exposure to artificial light, practice good sleep hygiene, and monitor your results.

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