this sounds corny, but here it is:
for all the talk of climbers dying, I don't really think that is what we are afraid of. I don't think overcoming the fear of death is that big of a step; however, overcoming fear of future suffering is a much stickier wicket.
the times I've been scared climbing (I mean sewing-machine leg, lizard-brain blubbering, breath-less outta control afraid) have been leading slabbyish, traversish trad and thin, last-3-placements-sucked aid. I've been lucky in that I have a supportive partner who always says I can back off if I need to. That helps. of course, it also helps knowing that oftentimes my only option is to keep going. That is when I realize the phrase "suck it up" actually has some merit; I've usually either stopped breathing or am on the verge of hyperventilating. I pause and make myself breath right, and make myself think only of my breathing. I think it is easier to tell the body first that there is no reason to be scared, then tell the mind.
Oh, and don't look down.