Well first, you're right, you can't _prove_ something like that to yourself. But in that case, what's the difference? (Unsolvable, usually irrelevant philosophical question, I suppose.)

Second, folks claiming to astral travel are, as far as I can tell, just lucid dreaming. Otherwise, we'd see more cults doing amazing things because they could go around and view secret plans, codes, passwords, and whatnot.