Polyphasic sleep

Polyphasic sleep is any sleep of multiple periods in the course of 24 hours. Polyphasic usually means more than two periods of sleep, whereas biphasic (or diphasic, bifurcated, or bimodal) sleep, means solely two periods of sleep. Its opposite is monophasic sleep, one period of sleep within 24 hours. The term polyphasic sleep was first used in the early 20th century by psychologist J. S. Szymanski, who observed daily fluctuations in activity patterns.

While today monophasic sleep is considered the norm, historical analysis suggests that polyphasic nighttime sleep, as in the sense of segmented sleep, was common practice across societies before industrialization. Although simians are monophasic, polyphasic sleep is common among animals, and is believed to be the ancestral sleep state for mammals.

Beside polyphasic nighttime sleep a common simple practice of biphasic or polyphasic sleep is having a nap, a short period of sleep during daytime, as an addition to nighttime sleep practices. Particularly when practiced on a daily basis, naps are sleeps taken between the hours of 9 am and 9 pm.

Polyphasic sleep can be a practice, but also a condition of interrupted sleep, as in the irregular sleep-wake syndrome, caused by a circadian rhythm disorder. Or it can be a practice of divided sleep. Polyphasic sleep, as in the sense of divided sleep, is also used as a term for a practice and its community of people experimenting with alternative sleeping schedules in an attempt to increase productivity. There is no scientific evidence that this practice is effective or beneficial, with research not recommending a fragmentation of sleep.