Normal Sleep 

• Sleep is a universal behavior that has been demonstrated in every animal species studied, from insects to mammals.

• It is one of the most significant of human behaviors, occupying roughly one-third of human life.

• Although the exact functions of sleep are still unknown, it is clearly necessary for survival because prolonged sleep deprivation leads to severe physical and cognitive impairment and, finally, death.

• Sleep is particularly relevant to psychiatry because sleep disturbances occur in virtually all psychiatric illnesses and are frequently part of the diagnostic criteria for specific disorders.

• The ancient Greeks ascribed the need for sleep to the god Hypnos (sleep) and his son Morpheus, also a creature of the night, who brought dreams in human forms.

• Dreams have played an important role in psychoanalysis.

• Freud believed dreams to be the “royal road to the unconscious.”

Electrophysiology Of Sleep

• Sleep is made up of two physiological states:

◦non-rapid eye movement (NREM) sleep
◦rapid eye movement (REM) sleep.

• In NREM sleep, which is composed of stages 1 through 4, most physiological functions are markedly lower than in wakefulness.

• REM sleep is a qualitatively different kind of sleep, characterized by a high level of brain activity and physiological activity levels similar to those in wakefulness.