Hm. I have a sleep walker, but she comes down the stairs, and navigates furniture, etc. quite well. She just is also talking to a friend who lives across town or telling her brother not to mess up her lego city... when he's in his bed asleep. From my research, sleep walkers aren't too likely to fall down stairs or walk into things because their eyes are open and they are processing those things.
I think that runs in families. My brother used to sleepwalk and my two brothers used to have entire, semi-coherent conversations in their sleep. Slightly odd ones with some disjointed bits, but mostly made sense, if you believed in pet dinosaurs and flying hotels. They never remembered them in the morning at all.
We've also braved night terrors, although not often and not with sleep walking or moving around beyond sitting up.