Sleep

Sleep is necessary for both humans and animals. Night is considered to be best for good sleep. Particularly dreamless sleep restores and recovers health more effectively than dreamy sleep does. Dreamless sleep is also called deep sleep. Adult humans need 6-8 hours of sleep per day. However, children and infants need more sleep than adults and elders do. Sleep deprivation causes many types of illnesses which result in a loss of efficiency and a deterioration in quality of life. Therefore, causes of sleep deprivation need be diagnosed and proper remedial/curative measures need be ensured.

It is believed that good dreams foretell the future in addition to replaying our past. But, unfortunately, very few people are able to interpret dreams. In the same way, very few people are able to forecast the future. Scientific and technological data may help improve interpretations regarding the near future.

Stages
Further information: Neural oscillation


 * Stage 1 (NREM): Stage between sleep and wakefulness, muscles are active and the eyes roll slowly, opening and closing moderately.


 * Stage 2 (NREM): Theta activity; in this stage, it becomes harder to wake up the sleeper. In this stage, the alpha waves of the previous stage are interrupted by abrupt activity called sleep spindles and K-complexes.


 * Stage 3 (NREM): This stage is called slow-wave sleep (SWS). SWS is initiated in the preoptic area and consists of delta activity. The sleeper is less responsive to the environment. Many environmental stimulations no longer produce any reactions.


 * Stage 4 (REM): The sleeper now enters rapid eye movement (REM) where most muscles are paralyzed. An adult reaches REM approximately every 90 minutes. REM sleep occurs as a person returns to stage 1 from a deep sleep. The function of REM sleep is uncertain, but a lack of it will impair the ability to learn complex tasks.