This stuff is what gets me in trouble. I don't have to let you do this to me. I can try counting backwards. At once it can cripple judgment, and unleash actions. It is a self-defense reflex.
Dramatic changes take place.
Blood flow is diverted from the brain and internal processing, saving the available supply for the large muscles needed for battle. The Immune System is down. Our senses are heightened. In this state we have reduced 'thinking' abilities. This reflex is triggered by a 'perceived threat'.