You know when you're drowning you don't actually inhale until right before you black out. It's called voluntary apnea. It's like no matter how much you're freaking out, the instinct to not let any water in is so strong that you won't open your mouth until you feel like your head's exploding. Then when you finally do let it in, that's when it stops hurting. It's not scary anymore, it's... it's actually kind of peaceful.