A sleep disorder in which one moves around, performing various activities, while asleep or nearly asleep; episodes are typically not remembered the next day. A family history of sleepwalking, also known as somnambulism, is often to blame, but stress or other psychological factors can play a role as well.
Example: A man’s wife sees him leave his bed without waking and wander through the house. After a few minutes, he awakens and quickly reorients himself.
This is an extremely comprehensive overview of the sleepwalking disorder, the symptoms and the causes: http://www.emedicinehealth.com/sleepwalking/article_em.htm