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 StagesSleep 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.