look up sleep paralysis... when you wake up in REM sleep but the paralysis doesn't immediately lift, you can have physical dissociation type episodes. Used to get 'em regularly as a teen and it went from terrifying to fun.I suspect the most common cause of things reported as OBEs
i started getting sleep paralysis a lot in my junior year of college but my OOBE experience happened way earlier, when i was 5, and i was knocked out from falling, not asleep