There are more than 80 different sleep disorders. The most common include apnea, insomnia, narcolepsy, periodic limb movements and restless leg syndrome. UCSF's Sleep Disorders Center is a specialized diagnostic clinic designed to evaluate patients with a wide range of sleep-related problems.
During sleep, we usually pass through five phases and complete several full cycles of these phases each night:
The first REM sleep usually occurs about an hour to an hour-and-a-half after we fall asleep. As adults, we spend almost 50 percent of our total sleep in stage 2 sleep, about 20 percent in REM sleep and the remaining 30 percent in the other stages.
When our sleep cycles are disrupted due to disease, medication, stress or physical problems, sleep deprivation can result. Sleep deprivation can interfere with work, driving and even social activities.