When our brain processes something as scary or dangerous, we act on it, upon the fight or flight response your brain releases epinephrine and adrenaline. Which gives you energy and pain tolerance. Other than that I can say that I've had this happen and I had a fight then flight response. You know when a dog jumps over a fence and is snarling at you it's scary. but I was on my bike, first instinct in my fight or flight category was to punch a rottweiler right in the snout, as soon as I heard it yipe then growl louder and bark the flight response finally kicked in. Man does the brain act weird.
