Does the area seem painful? Is it hot, was it swollen at all? "sagging" to me might imply that it was swollen at one point and went down very quickly, but the skin stayed stretched. Worse case scenario is that you quicked a nerve and the muscle needs a chance to go back to normal, or he is developing gangrene in that area (but usually the latter would result in major swelling and then peeling of the dead layers).
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."