How do you know you're not just dreaming right now?
But what kind of out-of-body experience do you mean? I've had strange little moments when I all the sudden get the sensation I'm over my body looking down. Have you ever had a hallucination? It's kinda like that. Not totally dream, but not totally real either. (If you want some hallucinations, just don't sleep for about 48 hours, of course, they may be weaker than drug-induced, but much safer, unless you want to drive somewhere. Don't try the drug kind (not to imply that I have, of course)).
Also, have you ever had a dream where you are looking at your body from a 3rd person perspective, but still seem to have control of it? It's also kinda like that. In fact, it's the way our memory sometimes works: we imagine a scene we were in from a 3rd person perspective, even if it didn't exactly happen like that.