Suspense just kills me!

What is it that makes bad things so bad? Isn't it mostly the anticipation? Like when you give blood - you feel the anxiety rising, so tight inside, thinking "What if the nurse is not properly trained and she pokes the needle where it's not meant to go? What if my veins burst or some other terrible thing, and blood goes everywhere? What if...?" You've been there before, and you know the pain of the prick will be so momentary, and there is a 99.999% chance that everything will be fine, and yet you toture yourself for so long about something you know will be okay!
Why???

I know that I only have to get through five minutes at a time, and that even if it's a bad 5min, I'll survive, it will be over and I'll forget about it. No matter what happens to me, I know I'll be okay, so why do I continue to worry? Why do I drag out the unpleasant and make it so much worse than it has to be?

Emotions are so irrational, and I get so frustrated with myself when I don't control them! I feel so feeble and weak! But maybe I'm just human...