Somnambulism is sleepwalking. Some people have managed to walk around their neighborhood without even knowing it because of somnambulism.
The roots of this word — somn and amublate — are related to sleep and walking, and that's exactly what somnambulism is: walking in your sleep. Lots of people engage in somnambulism every night, usually harmlessly. Somnambulism can also include talking in your sleep and doing other activities.