There are more than 70 different sleep disorders that are generally classified into one of three categories:
- lack of sleep (e.g., insomnia),
- disturbed sleep (e.g., obstructive sleep apnea), and
- excessive sleep (e.g., narcolepsy).
In most cases, sleep disorders can be easily managed once they are properly diagnosed. Insomnia is the most common sleep disorder. It occurs more often in women and in the elderly.
The amount of sleep that a person needs to function normally depends on several factors (e.g., age). Infants sleep most of the day (about 16 hours); teenagers usually need about 9 hours a day; and adults need an average of 7 to 8 hours a day. Although elderly adults require about as much sleep as young adults, they usually sleep for shorter periods and spend less time in deep stages of sleep. About 50% of adults over the age of 65 have some type of sleep disorder, although it is not clear whether this is a normal part of aging or a result of medications that older people commonly use.
Falling asleep and waking up are controlled by various chemical changes in the brain and in the blood. Foods and medicines that alter the balance of these chemicals also affect how well we sleep. Caffeine, for example, can cause insomnia (lack of sleep). Antidepressants can cause a loss of REM (rapid eye movement) sleep, as can smoking and alcohol. Smoking and alcohol also can result in a loss of deep sleep. Both REM and deep sleep are essential parts of the normal sleep cycle.