Polyphasic sleep

Polyphasic sleep is the practice of sleeping multiple times in a 24-hour period—usually more than two, in contrast to biphasic sleep (twice per day) or monophasic sleep (once per day). The term was first used in the early 20th-century by psychologist J. S. Szymanski, who observed daily fluctuations in activity patterns (Stampi 1992). It does not imply any particular sleep schedule. The circadian rhythm disorder known as irregular sleep-wake syndrome is an example of polyphasic 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.