SLEEP

Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than being in hibernation or a coma.

The purposes and mechanisms of sleep are only partially clear and are the subject of intense research. Sleep is often thought to help conserve energy, but decreases metabolism only about 5–10%.

Children need more sleep per day in order to develop and function properly :

 up to 18 hours for newborn babies, with a declining rate as a child ages.

 A newborn baby spends almost 9 hours a day in sleep.

Human sleep needs can vary by age and among individuals, and sleep is considered to be adequate when there is no daytime sleepiness or dysfunction. Moreover, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy.

  There is a explanation abaout sleep. I hope this explanation useful for us.