These include medical disorders such as ASTHMA, ANGINA PECTORIS or EPILEPSY which are made worse by sleep, and also a range of behavioural alterations which are usually related to a specific sleep stage or to a change from one state of sleep to another. Sleepwalking, night terrors, and nightmares are examples.

Difficulty in initiating or maintaining sleep. It affects around 15 per cent of the population at any one time, and is often due to a poor pre-sleep routine (e.g. taking excessive stimulants such as caffeine); unsatisfactory sleep due to poor environments such as an uncomfortable bed or a cold or noisy bedroom; anxiety and/or depression; or occasionally to a physical problem – for example, pain – or a medical disorder associated with sleep such as obstructive SLEEP APNOEAS or RESTLESS LEGS SYNDROME.

This is usually due to sleep deprivation caused either by inadequate duration of sleep, or by poor quality of sleep. The individual's lifestyle is often a cause and modification of this may relieve the problem. Other common causes of excessive daytime sleepiness are depression, obstructive sleep apnoeas, RESTLESS LEGS SYNDROME, excessive alcohol or other drug intake, and, less commonly, NARCOLEPSY.