Dreams often are exciting and full of action. In them you run, hit, jump, fall and maybe even fly. Dreaming about these actions is one thing. But physically doing them while you are still asleep is dangerous.

To protect you from hurting yourself, your body has a way of keeping you from acting out your dreams. It paralyzes most of your muscles during rapid eye movement (REM) sleep. This is the stage of sleep when you have most dreams and nightmares. If you wake up and recall a dream, chances are that you were in REM sleep.

During a dream, you may want to move. But your brain tells your muscles to stay still. A few muscles are allowed to work during REM sleep. This includes the eye and breathing muscles.

So what would happen if the brain did not turn off your muscles during REM sleep? In this case, you would talk, jump out of bed, hit and move about. In general you would act out whatever you were dreaming.

There is a good chance that you would either hurt yourself or someone else in the bedroom. You might fall out of bed, run into a desk, kick your bed partner, hit your head on a dresser, walk into a door or jump out of a window. Cuts, bruises, and broken bones would be likely to occur.

In some people, all of this really does happen. They have a problem called REM sleep behavior disorder (RBD). It is not the same as sleepwalking, which is much more common. Sleepwalking occurs during the slow-wave stages of deep sleep, not during REM sleep. Sleepwalking occurs most often in the first third of the night. When awakened, a sleepwalker is very confused and has no memory of the event.

RBD is more likely to occur later in the night. At the end of an episode, the dreamer quickly wakes up and is alert. He or she is able to recall the dream and describe it. The details of this dream match the unusual behavior.

RBD is more common in older people. It also appears more often in men than in women. But even young adults and children can have this happen. It can occur in perfectly healthy people once or twice in a lifetime. It is more likely to occur if you are overly tired, in a strange place or under great stress.

When it happens more often, it may be a sign of a neurologic disorder. It often is linked to Parkinson disease. You should talk to your doctor if you have had more than one episode of RBD. He or she may refer you to a sleep specialist.

By Dr. Richard S. Rosenberg
Updated August 25, 2006