REM sleep behavior disorder (RBD) is a parasomnia. A parasomnia involves undesired events that happen while sleeping.
RBD occurs when you act out vivid dreams as you sleep. These dreams are often filled with action. They may even be violent. Episodes tend to get worse over time. Early episodes may involve mild activity. Later episodes can be more violent. RBD is often ignored for years. At some point it is likely to result in an injury. Either the person dreaming or the bed partner may be hurt.
RBD can be confused with sleepwalking and sleep terrors. In these other disorders, the sleeper is usually confused upon waking up. He or she does not become rapidly alert. In contrast, it is normally easy to wake a person with RBD who is acting out a dream. Once awake, he or she is also able to recall clear details of the vivid dream.