I'm not sure that would be classified as a delusion per se. Maybe it is, I can't make that call. For me, my delusions stemmed from pretty well nowhere and were a bit odd (like cameras in the sky, a secret organization were watching my every move to recruit me because of my special abilities etc). It does sound like your son needs help though if it's reached what you described. It sounds like something that deeply troubles him and is really taking over. I'm not sure if it's a fear rooted in reality, but it does sound like fear for sure. I think others might be able to give more insight on this, though.