Sleep, once thought to be a long slumber is actually composed of different sleep stages. These sleep stages are part of the body's critical functions and are important to a person's health. If a person does not get enough sleep, they tend to become irritable and if the lack of sleep continues they incur a "sleep debt". Classical symptoms of sleep debt include physical, mental and emotional fatigue. Many studies have shown that an overall lack of sleep decreases a person's life expectancy. Yet it is also possible to fall asleep for several hours and yet wake up tired. In addition, some studies have shown that too much sleep may result in a higher mortality rate. Whether this is due to out of balance sleeping habits or just that depressed people sleep longer is not clear. In any case, a better understanding of the different sleep stages can help a person improve their sleep habits and get a better nights rest.

The Sleep Stages

Sleep is divided into two different types of sleep stages: Rapid Eye Movement (REM) and Non-Rapid Eye Movement. These sleep stages were first identified in 1937 by Alfred Lee Lomis and occur throughout the night in different discrete stages. Each stage has distinct characteristic physical and neurological features that are measurable. It is widely accepted that each of the sleep stages seems to serve a required and distinct function.

The sleeps stages occur in cycles throughout the night, typically progressing from the NREM stages in the order of N1, N2, N3, N2 then to the REM sleep stage. After the first cycle completes, the cycle starts over again. In each subsequent cycle, the length of each stage changes. Many medical conditions have been associated with interruption of the sleep stages. For example, people with depression tend to have shorter REM sleep stage. There is a lot of ongoing research on the affects of disturbances to the sleep stages on a person's health.

NREM Sleep Stages

child sleeping

NREM sleep is actually divided up into three stages: N1, N2 and N3. Studies have shown that t here few dream occur during the NREM stages. During the N1 sleep stages a person loses most awareness of the outside environment. The body relaxes and some people experience body jerks and rarely some hallucinations. If a person is woken up in this stage, they often report that they felt that they have not slept. In N2 sleep stages, a person loses complete awareness of their surroundings and there is very little physical activity. About half of an adult's total sleep is spent in this stage. N3 sleep is also called deep sleep. It is in this stage that sleepwalking and night terrors can occur and typically occurs in shorter and shorter durations during sleep.

REM Sleep

The REM is the most famous of the sleep stages. The REM sleep stage is when most of the dreaming occurs and averages about one quarter of an adult's sleep time. REM sleep is distinguished by rapid eye movements and rapid low-voltage EEG brain measurements. The body also tends to become very still and unresponsive. It is thought that this non-responsiveness is an evolutionary adaption to prevent us from harming ourselves by reacting or acting out to dreams that occur during this sleep stage. REM sleep has been associated with creative association process. Studies have also shown that sleep deprived people do not fall into REM sleep rapidly and do not stay in these sleep stages as long. Thus much research has centered on helping individuals stay in this stage or reach the stage sooner for a better night's rest.