I had horrible anxiety and it turned out to be a symptom of celiac disease
. It's an autoimmune disease
where anti- gluten antibodies
attack your intestines causing damage. Most of the serotonin in your body is located in your intestines so if they're damaged it can't use it. It's super common (about 1 in 100 people have it) and it can have random symptoms. I have actually spotted a few people on the celiac message boards who said that everyone thought they were hypochondriacs because they always felt sick but the doctor told them there was nothing wrong with them. Anxiety and depression
are the most common symptoms of it. The anxiety mixed with feeling vague symptoms will do that. I think you should have him try a gluten free
diet. It's the one autoimmune disease that is treated by diet, so if he has it, his symptoms go away. Even if he doesn't have it, he has something to focus on and will believe that his disease is going away because he is treating his "disease". I also lost 20 pounds when I cut out gluten, so it might help with his weight as well.