The following is a list of stages of a healthy night’s sleep and what occurs during these stages:
Non-REM sleep
Stage 1 -
Occurs in the beginning of sleep, with slow eye movements. People in this stage often believe that they are fully awake. During the transition into Stage 1 sleep, it is common to experience a hypnic jerk.
Stage 2 -
The person is unconscious, though awakened easily. No eye movements occur, and dreaming is very rare during this stage. EEG recordings tend to show characteristic “sleep spindles” and “K-complexes” during this stage.
Stage 3* -
Transition between stage 2 and stage 4. Delta waves begin to occur.
Stage 4* -
Slow-wave sleep referred to the “deepest” stage of sleep. Dreaming is more common in this stage than in other stages of NREM sleep though not as common as in REM sleep. The content of SWS dreams tends to be disconnected and not as vivid as those that occur during REM sleep. This is also the most common stage in which parasomnias occur.
* This is deep-sleep part of the sleeping period. During these stages our blood pressure and heart rate reach lower ranges, providing rest for the cirulatory system and helping to ward off cardiovascular disease. Some researchers suggest that newly acquired information is consolidated as part of our long-term memory at this point.
The production of growth hormone peaks during the non-REM sleep, with some teenagers producing as much as 50 times more growth hormone at night than during the day.
REM sleep
Stage 5 -
Rapid eye movement (REM) sleep is the stage of sleep characterized by rapid movements of the eyes. During this stage, the summed activity of the brain’s neurons is quite similar to that during waking hours; for this reason, the phenomenon is often called paradoxical sleep. Most of the vividly recalled dreams occur during REM sleep.
During a healthy night’s rest REM sleep occurs several times, alternating with non-REM sleep. Most of the dreaming occurs during this stage. Maximum muscle relaxation also occurs at this point, which allows the sleeper to wake up feeling physically refreshed.