Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A sleep disorder (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 and emotional functioning. A test commonly ordered for some sleep disorders is the polysomnogram. The most common sleep disorders include: primary insomnia, a chronic difficulty in falling asleep and/or maintaining sleep when no other cause is found for these symptoms. Bruxism, involuntarily grinding or clenching of the teeth while sleeping etc.