hello, i can understand your concern. head injury and blood in stools dont seem to be related unless he had any injury in the anal region which doesnt seem to be present based on the history given. since your son had a black out after the injury and still complains of headache i would suggest to go to an ER and get a C.T scan of the brain done to rule out any bleeds. i would assume the bleeding in the stools to be fresh based on the symptom. if this is one off you need not worry, if the problem persists and if loose stools are also present it might be an infection, a stool test is advised for the same. none the less a thorough physical assessment is advised so that presence of any other conditions like hemorrhoids is ruled out. a diet rich in fiber is advised. hope i have answered your queries . feel free to ask further queries. thanks for choosing HCM