As a kid I watched the needle go in my arm as blood was drawn.... and all of a sudden tunnel vision and almost fainting. Had to be walked to the car.

So I figured out watching blood come out of me causes me to feel faint, so I don't watch. I've seen blood and other person's blood, but my blood seems to be some special case.

What I've figured out is - if you are bleeding, maybe your brain helps you collapse to the ground in a faint, where you will be level, have a low heart rate, and not bleed out all your blood through a wound.

Could this be the evolutionary reason we faint at the sight of our own blood?