A recent article http://www.nytimes.com/2012/04/17/science/studying-states-of-consciousness.html talks about experiments involving different states of consciousness. Based on this article I hypothesize is that if you 'wake' a sleepwalker, you're then interacting with someone whose 'higher' brain function (i.e. the neocortex: I assume you know what that is) isn't active and in control. IMO whether that's 'dangerous' depends on the situation, i.e. on the people in question and how they interact (and on which of the two of you is the stronger etc.). My personal experience is that I have less patience, more likely to be lacking in self-control, and more likely to react or overreact to (for example) any perceived violence (of yours) with violence of my own, when I'm dead tired, half-, or more-than-half-asleep. I won't retreat (I say "retreat" in the context of http://en.wikipedia.org/wiki/Stand-your-ground_law) may not take stock of a situation: when I am barely awake, and in my own home. It's the only situation I remember, in the last 10 years, that I've hit or pushed a person. It's usually safe to come and pester me while I'm asleep, but I'm probably more like an (large) animal than a 'person', for as long as I'm only semi-conscious. So IMO it could be dangerous and I wouldn't recommend it. The two viewpoints you quoted don't seem contradictory to me: - One says to be nice/compassionate to a person who is needing their sleep - The other says that if you wake them, they'll be disoriented. Dealing with a drunk may be a similar situation, IMO. Your other quote (TvTropes) says, "it's an old wives' tale that still persists despite scientific evidence to the contrary". --- Edit: I believe the above answer is true and useful, but too personal and unresearched, so I have marked it 'community wiki', in case you want to edit/improve it. I found the initial citation/article interesting.