I very strongly suspect that your son's "condition" is, in fact, a response to the stress and anxiety he senses.
Kids don't always have words---and their bodies do the talking.
When my son was in his early teens, he had PROFOUND physical effects. They actually began before d-day; he was aware of what was going on before I was, poor kid.
He developed serious, unremitting vomiting, then migraines. I mean, brain-scan, stomach-biopsy illness. It persisted over the course of two school years. Then d-day hit---and it all became clear: it was DEPRESSION.
The MINUTE I said to him, "P, I think this is depression," it was like a weight was lifted from him. The headaches and vomiting remitted immediately.
Unfortunately, they were replaced with crushing symptoms more typical of depression---and it was VERY scary.
It was very rocky time, but with appropriate care, has improved dramatically. Now I have my "old" boy back.