I think if the acid is caused by stress/anxiety, he shouldn't have trouble with it after he's learned to handle it through therapy. Sometimes though, people just have trouble w/ acid regardless of stress.
When I was in college, I also suffered from panic disorder, so I really feel for your son. It's an awful thing to live with. I saw a therapist that specialized in anxiety disorders, and after (can't remember how long I went to therapy) I was panic free. Have been for nearly 20 years, so tell your son it doesn't have to be like this forever.
I didn't have problems with acid back then- but I do now. If the Zantac doesn't work, the gastroenterologist can give him something a lot better. He also needs to be better about his diet (at least until the acid is well controlled) because the acid will make his life miserable. I'm sure you already know to avoid anything spicey or acidic, but he should also avoid soda and ibuprofin (if at all possible).
Best wishes for your son! :)