Although REM is a stage of deep sleep in which muscles are very relaxed, paradoxically, people in REM sleep and people who are awake have similar brain wave activity.
The activation-synthesis theory of dreams states that neurons in the brain randomly activate during REM sleep and that dreams arise when the cortex tries to make meaning out of these random neural impulses.
The classes of recreational drugs are stimulants, sedatives, hallucinogens, narcotics, and cannabis-derived drugs.
One theory proposes that hypnosis causes people to dissociate or divide their consciousness into two parts: an observing part and a participating part. Another theory proposes that hypnosis makes people play elaborate roles.
The functions of sleep include conservation of energy, protection from predators, and restoration of body tissues.