Intrinsic sleep disorders

12. Restless legs syndrome

This syndrome is characterized by uncomfortable feelings (tingling, itching, crawling, pulling, or aching, for example) in the legs right before falling asleep. These feelings are relieved by moving the legs but return when movement stops. This interferes with falling asleep and can cause severe insomnia.

(Source: Promise of Sleep by William C. Dement, Delacorte Press)