Anger raises your blood pressure. That leads to the effects that @WillWorkForChocolate talks about. When you get angry, the adrenaline pumps. Your body readies itself to do whatever is needed, instantly. If you have PTSD, your body is trained to initiate this response instantly and at a much lower threshold than for most people. Anger actually takes time off your life, and gives you a higher risk of heart disease and heart attack and that sort of thing.
The headaches are a part of it. Constriction of blood vessels in your head is probably what leads to the headaches. All part of the flight, freeze or fight response. It is actually worth learning how to reduce your anger response. Makes you live longer.