A Sleep Disorder, or Somnipathy, is a medical disorder of the sleep patterns of a person or animal. Some sleep disorders are serious enough to interfere with normal physical, mental, social and emotional functioning. Polysomnography is a test commonly ordered for some sleep disorders.
Disruptions in sleep can be caused by a variety of issues, from teeth grinding (bruxism) to night terrors. When a person suffers from difficulty falling asleep and staying asleep with no obvious cause, it is referred to as insomnia.
Source: http://en.wikipedia.org/wiki/Sleep_disorder
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