Other forms: sleepwalking; sleepwalks; sleepwalked
To sleepwalk is to walk around despite being sound asleep. If you wake up outside in your PJ's, then, chances are, you were sleepwalking.
A fancier word for sleepwalk is sonamubulate, and the act of sleepwalking is known as sonambulism by doctors who study and treat sleep disorders. It's considered a disorder to sleepwalk because normally your sleeping brain keeps you from performing actions like walking (even when you dream that you're walking). In Shakespeare's play Macbeth, there is a famous scene in which Lady Macbeth sleepwalks because of her guilty conscience.