Sleep cannot be considered a passive absence of function but is an essential process during which our brains and bodies regenerate. It is characterised by many disparate active processes referred to as rem sleep and non-rem sleep that occurs in ninety-minute cycles. 

We need about five cycles of sleep per night which equates to seven to nine hours of sleep per night.  Melatonin from the pineal gland triggers our sleep, but there are many other factors that contribute to our sleep-wake cycle. 

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