A dyssomnia is a disorder of getting to sleep or staying asleep or of excessive sleepiness. The person typically experiences changes in the amount and/or timing of sleep, and how restful it is. The dyssomnias are disorders of sleep or wakefulness, in contrast to parasomnias, which are about the sleep/wake transition.
Dyssomnias include extrinsic (caused by factors outside the body), intrinsic (caused by factors inside the body), and circadian-rhythm sleep disorders. When people say they have sleeping problems, they usually are referring to one or more dyssomnia.
Sleep state misperception
Circadian-rhythm sleep disorders