I had this happen to me one time with a muzzleloader. I shot at about 80 yards and dropped a big buck. I shot him in a large shooting lane and he went down and was flopping around and moved himself out of the lane. I waited about an hour, went over expecting him to be right below the lane and he was no where to be found. Searched all over and didnt find him. Sometimes you clip the spine and temporarily paralyze them but they get back to their feet and make it. Ever since this happened to me I make sure to get another shot in the deer if I can. Just gotta learn from experiences. good luck