What causes sleepwalking?

Mumbling fantastical gibberish; devouring blocks of cheese in the nude; peeing in places that aren't toilets; and jumping out of windows. These are all things people have reportedly done while sleepwalking, a behavior that can be dangerous in some cases. It's estimated that around 18% of people sleepwalk at least once in their lives. So, what exactly is sleepwalking? Emmanuel During investigates. [Directed by Laura Jayne Hodkin, narrated by Jack Cutmore-Scott, music by Salil Bhayani, cAMP Studio].