Sleep is an altered state of consciousness where awareness of surroundings is decreased and there are few voluntary body movements. There are three processes underlying the regulation of sleep – the homeostatic, circadian and ultradian – and each of these is regulated in turn by hormonal, neurological and environmental factors. The importance of sleep has been shown by the problems a lack of sleep creates.
There are five stages in a normal sleep cycle, the first four of which are non-REM or rapid eye movement, and the last REM or rapid eye movement.
- Manifested by a feeling of drowsiness, a measurement of brain activity shows fewer alpha waves and the appearance of theta waves.
- Almost no awareness of the environment and low EMG.
- An appearance of delta waves seen as a transition to the fourth stage.
- Deepest stage of sleep which takes up about 10-15% of sleep time.
- REM sleep associated with dreaming and usually occurs in the final third of the sleep period.
The amount of sleep an individual needs is biologically determined but an average of eight hours is recommended. Sleep deprivation can cause psychological and physical problems ranging from irritability and poor judgement to obesity, heart attacks and cancer. Not getting enough sleep affects the immune system and so infections are more likely.
Too much sleep, which is anything over fourteen hours in one session, can also cause problems such as dizziness and lack of muscular control.
There are three types of sleep disorders. Dyssomniacs have difficulty in falling to sleep; parasomniacs wake while sleeping and the third group comprises disorders resulting from psychiatric problems.