The fear of incapacitation is a very valid one. My step-dad died in a motorcycle accident and the head injury was very bad. They still tried for over an hour to resuscitate him... My mother was very upset, because if they had succeeded he still wouldn't have been alive (mentally.)

Other than head injury or spinal injury I'm not sure how one would become incapacitated hiking (not including climbing here).. but please don't enlighten me! I don't need anything else to worry about