apprently drowning's not that bad..i know a couple of people who very nearly drowned, they said after a while it just feels kinda peaceful.Still,it must be nasty!
How about being in a room where two of the walls are very slowly moving inwards,crushing you to death and theres no way to escape.Think about it,what ever you do your body's going to turn and your head's gonna get crushed first.The slower the walls are moving, the more painful and drawn out its gonna be.
For some reason,i think about this quite a lot :s