this is a surefire way to stop it, no bullshit.
**** i woke up with a bloody nose this morning actually, at 3 am.

pinch the middle of your upper lip
your thumb on the inside, pointing finger on the outside and pinch where the kind of U shaped thing on your upper lip is (if you have that)

my friend who is a training paramedic told me this. i guess thats what they do.
it stops a nosebleed in 30 seconds, no joke.