Dream Dictionary

Sleep paralysis is a term either used to describe the normal paralysis of the body that occurs during REM sleep, or a disorder where awareness is maintained when the body becomes paralysed when entering sleep (known as hypnogogic paralysis) or remains inappropriately paralysed when awakening (known as hypnopomic paralysis).

 It is especially common in those suffering from narcolepsy although most people experience sleep paralysis once or twice in their lives and is usually considered as harmless, although can be a frightening experience for many people. When frightening, it can be accompanied by feelings of helplessness, and people have reported the feeling of a malevolent "presence," or the sensation of being held down or otherwise forcibly restrained, often as a pressure on the chest. The state of paralysis may continue for several seconds or even minutes.

Many sufferers report very vivid hallucinations during this state. These often take the form of seeing or sensing a 'presence' in the room, which may sometimes be linked to the feeling of being restrained. Hallucinations are also common the hypnagogic and hypnopompic states and their presence in awareness during sleep paralysis may be due to the same processes.

Little is known about the physiology of awareness during sleep paralysis. However, some have suggested that it may be linked to post synaptic inhibition of motor neurons in the pons region of the brain. In particular, low levels of melatonin may stop the depolarisation current in the nerves, which prevents the stimulation of the muscles.

In Japan, sleep paralysis is referred to as kanashibari; in Canada, as a visit from the "old hag." In medieval times, attacks of sufferrers of sleep paralysis may have given rise to the belief in incubi, succubi and other demons.

The combination of paralysis and hallucinations has led some to speculate that sleep paralysis might be a cause of some alien abduction reports and other paranormal experiences.