Sleep is one of the most mysterious of all human activities. Exactly what happens during sleep is still not completely understood. By studying brain wave patterns, sleep researchers have identified four separate stages in a normal period of sleep. Stage 1 begins when we first fall asleep. Stage 1 is light sleep. Muscles relax and the heart slows down in stage 1. During stage 2,the heart rate increases. Stage 2 sleep is called REM sleep because of the rapid eye movements that occur during this stage. The autonomic nervous system is active in REM sleep, causing rapid breathing
and increased stomach acid secretion. Stage 2 is the period when we dream. During deep sleep (stages 3 and 4), no dreaming occurs. In a normal sleep period, a person cycles from stage 1 to stage 4 in about 90 minutes. Waking after one full sleep cycle is complete is common among the elderly and small children.
Here is an older video, the first in a series on the physiology of 'dreaming'. Very interesting. Watching it made me conscious of the importance of good nutrition and getting enough rest-- not to get to a state of un-health where psychotropic drugs are prescribed, and, if you do find yourself there, to take a look at what you can do to reclaim your health and ability to relax and rest properly.
Here are the other videos in the series: