Sleep and dreams fascinated people from different walks of life. Though sleep has been investigated over a century, questions such as ‘what physiological functions are carried out by sleep’ or why do we need to sleep? still remain to be debated. We need 7–8 h of sleep to keep us active throughout the day without feeling sleepy. Such constant daily quota of sleep is maintained through a balance between sleep duration and intensity by sleep homoeostasis. Sleep is important for energy conservation, immune regulation, learning and memory etc. and, hence, important for health and survival. Sleep disturbances during development have been correlated to the poor psychological and cognitive functions. Sleep deprivation on the other hand can be fatal too. This mini review provides the reader a bird's eye view on the functions of sleep.
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