Insomnia

Insomnia is the most common of all sleep complaints. Almost everyone has occasional sleepless nights, perhaps due to stress, heartburn or drinking too much caffeine or alcohol. Insomnia is a lack of sleep that occurs on a regular or frequent basis, often for no apparent reason.
How much sleep is enough varies. Although 7½ hours of sleep is about average, some people do fine on 4 or 5 hours of sleep. Other people need 9 or 10 hours a night.
Inability to get a good night's sleep can affect not only your energy level and mood but your health as well because sleep helps bolster your immune system. Fatigue, at any age, leads to diminished mental alertness and concentration. Lack of sleep is linked to accidents both on the road and on the job.
About one out of three people have insomnia sometime in their life. Sleeplessness may be temporary or chronic. You don't necessarily have to live with sleepless nights. Some simple changes in your daily routine and habits may result in better sleep.

(Disponível em: <http://www.mayoclinic.com> Acesso em 11 abr. 2003.)