A sleep cycle
is defined by a segment of Non-Rapid Eye Movement (NREM) sleep, which comprises of four stages, followed by a period of Rapid Eye Movement (REM) sleep. A typical sleep cycle is about 100 - 110 minutes long, beginning with NREM sleep and transitioning to REM sleep after 80 - 100 minutes. REM sleep
is accompanied by bursts of Rapid Eye Movements. It has heightened brain activity and temporary paralysis of the muscles that controls posture and body movement. REM sleep is otherwise referred to as the 'dream sleep'
as most of our dreams occur during this phase of sleep and the temporary muscle paralysis that occurs during this phase is a protective mechanism so that we do not act out our dreams.
Victims of REM Behavior Disorder (RBD) do not experience muscle paralysis,
which is the usual case during REM sleep. This gives the victim a free hand to physically demonstrate or act out dreams.
Patient with RBD demonstrate their dreams with passion and intensity, which can also turn violent. Many such patients sit up in sleep, make wild gesticulations, kick or scream, even punch their partner as they act out their dreams. Such behaviors can also manifest during withdrawal from alcohol or hypnotic drugs.