This guide is an exploration of sleep: the time of deep rest during the body's natural 24 hour circadian rhythm cycle. Here you will find information on the science of sleep, including peer reviewed articles on sleep and mental health, academic journals, and media on subjects such as sleep apnea.
All multicellular animals cycle through daily fluctuations in biological activity known as circadian rhythms, with the alternation of sleep and wakefulness being the most obvious example. In humans, a polycyclic sleep/wake cycle—several periods of sleep and arousal during a twenty-four-hour period—becomes evident in the fetus during the latter stages of pregnancy. As children progress from infancy through childhood, they gradually settle into a mainly diurnal pattern, with one long period of sleep during the day. A complex interaction of several external and internal events determines the timing and duration of sleep.