In the fight-or-flight response, the objective is to get away from the source of threat. All of our muscles prepare for this escape by increasing their tension level, our heart rate and respiration increase, and our whole basic metabolic system is flooded with adrenaline. Blood is diverted to the muscles, away from the viscera. The goal is to run away, or if we feel that we can't escape or if we perceive that the individual that's trying to attack us is less strong than we are, to attack them. Or if we're cornered by a predator—in other words, if there's no way to escape—then we'll fight back. Now, if none of those procedures are effective, and it looks like we're going to be killed, we go into the shock state, the tonic immobility. Now the key is that when people get into this immobility state, they do it in a state of fear. And as they come out of the immobility state, they also enter a state of fear, and actually a state in which they are prepared for what sometimes is called rage counterattack. For example, you see a cat chasing a mouse. The cat catches the mouse and has it in its paws, and the mouse goes into this immobility response. And sometimes you'll actually see the cat bat the mouse around a little bit until it comes out of the immobility, because the cat wants the chase to go on. Now, what can happen is that the mouse, when it comes out of the immobility state, goes into what is called nondirective flight. It doesn't even look for where it can run. It just runs as fast as it can in any direction. Sometimes that's right into the cat. Other times, it will actually attack, in a counterattack of rage. I've actually seen a mouse that was captured by a cat come out of the immobility and attack the cat's nose. The cat was so startled it remained there in a state of shock while the mouse scurried away. When people come out of this immobility response, their potential for rage is so strong and the associated sensations are so intense that they are afraid of their own impulse to strike out and to defend themselves. Again, this all goes back to our animal heritage.
People experiencing PTSD will sometimes exhibit outburst of anger and rage. The angry outbursts and aggressive behavior can occur because the individual relives the trauma (recreates the event as a flashbacks) and this drives them back into a state of fear-induced immobilization. When they return back out of the tonic immobility state, they can vent the stress energy in a rage counterattack. In this state they can mindlessly attack and harm others, including their loved ones.