I was reading up on Edgar Cayce and he predicted he would die if he kept Astral Projecting more then twice a day. Well it was world war II and mothers wanted to know if their sons would be safe in war, so Cayce couldn't refuse to help them. He kept projecting until he died right when he predicted.
So does this mean that if Astral Projection, or even any psychic ability, is over used dangers can be caused to the body?

I can't say for sure. If someone meditates too long without eating or DRINKING(drinking is really important. Especially water) that can be unhealthy. Personally I think the experience is different for almost everybody. That was Edgar Cayce. But some people(especially witches) performs astral projection like 24/7 without jack happening to them. I do think over-doing psychic abilities can be psychologically unhealthy. It can make you mentally tired and gives you headaches. But the limit is not the same with everyone. Some people can get easily tired when using a psychic ability for short time and some people can go longer. But you can build up your extrasensory muscles with training slowly and be able to perform your things longer such as many famous psychics and mystics. And remember, Edgar Cayce used to go in trance for a long period of time. That might have took him off of his 'humanity' sorta speak.