As many others have mentioned I feel more specific information is necessary to properly assess the situation. The armed guard idea might work but start by just sleeping in the same room as your son so as not to frighten him with a military like person he is unfamiliar with. I also agree with the basement idea though I am skeptical as to how effective it may be, especially if you have basement windows or a sliding glass door. Dragonrider suggested leaving him in the basement I would like to say that you should only do this if you are staying down there with him, we are trying to help him not scare him even more by leaving him down there alone. I do not feel that the video camera idea will be successful. In numerous abduction stories people report electrical equipment such as radios and video cameras to stop working. You may as well set up the cameras anyway though, it wouldn't hurt to try it. I also agree that you should see your local physician and request X-rays, look for anything out of the ordinary no matter how small. The vacation idea couldn't hurt definitely head for a city.
Like I said at the beginning of this post people are willing to offer their ideas but you must provide more specifics about the situation for anyone
to really help. Also I would like to say that IF this is a hoax then this person should be ashamed of themselves.