I for one always, always feel better after exercise. The morning after days I exercise pretty hard, my headaches seem to be milder than if I go a couple days without getting my heartrate up. I don't know why/how, but everything is better after a 30 min run, a soccer game, or a 2 hr bicycle ride. Your mileage may vary, but I don't think a completely sedentary lifestyle is healthy, even with a concussion/PCS.