If he can't feel or move things, stops breathing, goes unconscious, immediately call 911, DO NOT move any part of his body as this could cause much worse damage. If he can feel everything fine, didn't hit his head, and is speaking and moving normally, a 20-foot fall can cause internal injuries that don't present themselves right away. So go to the doctor or hospital as soon as you can to get checked out. If he for whatever reason declines going to the doctor, monitor him consistently for any changes in habit.
