It is known, however, that sleep consists of two very different states. Dreams occur during REM sleep and sexual arousal is common, even if the dreams themselves are not sexual in content. Periods of REM sleep last about 20 minutes and occur four or five times during the night. They alternate with longer periods of non-REM sleep, when the body function slows down. As the night foes on, the periods of non-REM sleep become progressively lighter.
Sleeplessness is also common during pregnancy, especially in the later weeks.
People with serious conditions such as asthma are unable to sleep because they fear dying in their sleep. For still others, the cause of insomnia may be attributed to their social environment. In the majority of cases, however, the core problem is emotional. Anxiety and internalized, unexpressed anger are common causes of sleeplessness. Paradoxically, insomnia may result from the use of a sedative prescribed to relieve it.