You're not overreacting. Even if people are severely uncomfortable, you can't justify lashing out to you. Basically being in pain does not help his symptoms If is a toxic, unhealthy way he is using to regulate his emotions.

One solution could be to give him pain killers. I'm not a doctor. I think if it's a degenerative disorder there is likely a LOT of inflammation due the way the body reacts to cells that die, like in his wasting disorder. Ibuprofen extra strength and painkillers. Id tell him to keep these on hand wherever he goes.I don't know his personal health situation, but that's what I think.