Somnambulism

In a state of deep sleep when there are no rapid eye movements to indicate dream, the person appears to respond to his surroundings and may carry out difficult or even dangerous tasks while apparently being unconscious of what is occurring, or at least being unable to recall events afterwards. Activities may be impossible to reproduce in the waking state (walking along a high ledge, singing the whole of a piece of music only heard once). Somnambulism seems to occur in response to an abnormal response of the nervous system.