Polyphasic sleep

Polyphasic sleep or segmented sleep is the system of sleeping during multiple periods over the course of 24 hours, in contrast to monophasic sleep, a single period of sleep within 24 hours. Polyphasic usually means more than two periods of sleep, as distinct from biphasic (or diphasic, bifurcated, or bimodal) sleep, meaning two periods of sleep. 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 the norm, historical analysis suggests that polyphasic nighttime sleep was common practice across societies before industrialization. Scientific experiments and observational studies have supported a theory of biphasic sleep in humans. Polyphasic sleep is common in many animals, and is believed to be the ancestral sleep state for mammals, although simians are monophasic.

A common practice of biphasic sleep is a nap, a short period of daytime sleep in addition to nighttime sleep. An example of involuntary polyphasic sleep is the circadian rhythm disorder irregular sleep-wake syndrome.

The term polyphasic sleep is also used by an online community that experiments with alternative sleeping schedules in an attempt to increase productivity. There is no scientific evidence that this practice is effective or beneficial.