A Clinician's Guide to Sleep DisordersAbout This Hardback Sleep disorders influence or disturb the sleep pattern of a person. They are broadly categorized into 3 groups, namely, dyssomnia, circadian rhythm sleep disorders and parasomnias. The most common type of sleep disorder is insomnia, which falls under the category of dyssomnia. A person suffering from this disorder has difficulty in falling asleep or getting adequate amount of sleep. A sleep disorder that causes a frequent need to