Sleep is a resting state for both the mind and body where most external stimuli are blocked. Most adults need about 6 to 8 hours of sleep for peak daytime alertness and energy.
During the nights sleep, a normal, healthy person alternates between non-REM and REM sleep 4 to 5 times a night.
Non-REM sleep makes up about 75% of the nights sleep. In non-REM sleep there are 4 stages of sleep, ranging from light to very deep sleep.
Stage 1 - non-REM sleep is a transition period from wakefulness to sleep. It can be described as dozing. During this period, breathing becomes steady, and the individual falls into a light sleep from which he/she can be easily awakened.
Stage 2 - non-REM sleep comprises approximately 45% of non-REM sleep. This is considered to be the onset of real sleep. Eye movements stop and brain waves indicate that sleep has officially begun.
Stage 3 - non-REM sleep comprises approximately 12% of non-REM sleep. In this stage, sleep becomes progressively deeper and the sleeper becomes more difficult to arouse.
Stage 4 - non-REM sleep comprises approximately 13% of non-REM sleep. It is characterized by very deep sleep. If awakened during this stage, a person will often feel groggy and disoriented for several minutes.
The differences between Stage 3 and 4 are difficult to determine and depend upon interpretation of brain wave characteristics.
Stage 3 and 4 are very important for the physical restoration of the body's immune function and repair such as muscle repair after injury and exercise. Also the body's greatest surge of growth hormone occurs in stage 3 and 4. This is particularly important for children.
REM sleep comprises the other 25% of a nights sleep. Most dreaming takes place during REM sleep. REM sleep is very different from non-REM sleep. During REM sleep there is periodic eye movement and eyelid fluttering, and irregular breathing. Body temperature falls and heart rate and blood pressure become irregular. During REM sleep, the brain blocks muscle activity so that the dreams will not be acted out. This includes blocking some muscle activity in the throat, potentially allowing the airway to collapse.
The purpose of REM sleep is thought to be for memory consolidation and brain maintenance.
Interruptions during sleep
Sleep is a necessary biologic function. Sleep patterns should not be interrupted. However, loud snoring or sleep apnea episodes can disrupt the normal sleep cycle patterns. Less time is spent in the valuable restful stages of sleep.
Without sufficient restful sleep, individuals become irritable and unable to concentrate. Work performance is likely to become impaired and there is excessive daytime drowsiness. Sleep deprivation is a significant factor in traffic and workplace accidents. 24 hours of sleep deprivation can be compared to a blood alcohol level of 0.1%! (legally impaired in some jurisdictions)