That's actually a very interesting thing, and one I don't understand. How come sometimes when we dream of being underwater we can't breathe for a while? It seems like I've had dreams where I was beginning to drown, and I wasn't breathing, until/unless I made some sudden convulsive effort and found I could breathe, If pinching your nose shut doesn't stop you from breathing in a dream, how can we feel ourselves drowning, even just for a moment? Maybe those are sleep apnea? (I think that's what it's called, when you stop breathing for a moment while sleeping). Or maybe like I surmised on another thread it's possible to close off your sinus passages (the handsfree nosepinch I brought up) - I can sure do it when I'm awake if I want to, and in sleep paralysis (or REM atonia to be more precise) we're only apparently paralyzed from the neck down, so maybe it is possible to close off the nasal passages in a dream? (hell, maybe that's what sleep apnea IS?! ~ either closing it off because we deam we're underwater, or maybe it just closes off involuntarily, like it can when nasal passages are swollen shut or like they do momentarily when we snore.)

Ok sorry, went into pontification mode for a minute there!