During REM sleep a part of our brain keeps us from moving our arms and legs, although we can still breathe and move our eyes. When the normal movement inhibiting mechanism fails, some people, usually men over age sixty, may develop REM sleep behavior disorder, and are able to act out their dreams. The risk of developing REM Sleep Behavior Disorder increases with age, and men are more likely than women to develop it. Sleep terror is a sudden arousal from slow wave sleep with a piercing scream or cry, accompanied by profuse sweating, and intense fear. It's not a dream or nightmare, but rather like having a panic attack in your sleep.
Sleep terror is especially frightening, because unlike nightmares, it occurs without dream recall.
People experiencing sleep terror do not know how they became so frightened. Sleepwalkers do not appear to be sleeping, but they are deeply asleep. Their eyes are typically wide open, with dilated pupils. Sleeptalking can also be observed during sleepwalking episodes. The episodes may or may not be associated with sleep terror.