John Coles wrote an interesting post on his blog on the fight or flight response. Read it here.
In previous posts, I've touched on the fight or flight response, the survival mechanism and the adrenaline dump that occurs during combat or extreme stress. It's important to incorporate some form of stress induced training to your regimen, and to understand what may or may not happen to you.
Equally important, and often overlooked, is understanding that your attacker may be experiencing all these same things, making them temporarily stronger and more resistant to pain.