During normal REM sleep, your brain sends signals that temporarily paralyse most of your voluntary muscles — a mechanism called REM atonia, which exists specifically to stop you from physically acting out what you're dreaming. In REM sleep behaviour disorder (RBD), that paralysis is incomplete or fails, and dream content translates into real physical movement.
What it actually looks like
This isn't sleepwalking calmly around a room — RBD movements are typically sudden, forceful, and match the content of an action-heavy dream: punching, kicking, shouting, or leaping out of bed, usually in response to a dream involving being chased or attacked. Unlike sleepwalkers, people with RBD can often be woken during an episode and will usually recall a vivid, matching dream afterward.
How it's different from sleepwalking
Sleepwalking happens during deep non-REM sleep, involves the whole body moving somewhat purposefully around an environment, and people are difficult to wake and rarely remember it. RBD happens during REM sleep specifically, involves more violent, dream-matched movement confined largely to the bed, and the dream content is usually clearly recalled.
Who it affects
RBD is significantly more common in men over 50, and it has a notable medical connection worth knowing about: it can precede the development of certain neurological conditions, sometimes by years, which is why doctors take a new RBD diagnosis seriously even when it seems like "just" a sleep issue. It can also occur as a side effect of certain antidepressant medications, or alongside other sleep disorders.