Losing appetite after returning home from overseas?

Part of the miltary inproccessing after being deployed overseas involves some sort of medical check up, my good friend tells me. He was just in Qatar for four months, and had, in fact, lost his appetite when he got back home. But he thought it was weird that the doctor asked him if that had happened. So, is there an explanation? Or does this just happen when one returns from being deployed?

FWIW, I have traveled overseas, voluntarily, many times and don’t remember ever losing my appetite upon return. But maybe it should have? Or I was just glad to have familiar food so I didn’t notice?