Theres theory that REM sleep,(rapid eye movement dreaming sleep as opposed to none REM paradoxical none dreaming sleep) evolved as a survival mechanism,apparently one can come awake instantly from REM sleep ready to flee or fight should old Mr Sabre Tooth come sniffing at your sleeping bag, whereas from none REM sleep, should you be rudely awakened yer buggad and confused, noticed meself that I always seem to wake from a dream,perchance you are waking up from paradoxical sleep Boss another timing error I would say.
Tiz called paradoxical sleep I believe because it seems to have no purpose,deprive somebody of REM sleep, ie keep waking em up when their eyes begin to move and they quickly go off their chumps,waking folks up during none REM sleep doesn't seem to make a blind bit of difference, so they have come to the conclusion that REM sleep is necessary and tother kind is just a hangover from our single cell amoeba days, of course, they are probably wrong.
Drapes and the Woo person had a long and facinating thread about the Human mind and what dreams actually are, twas a while back though, we even had Danny interested, and that takes some doing.