@@, he snapped at you. And now you're losing sleep over him. I am sympathetic to disabilities. However, from the sounds of it, he has been completely unwilling to do anything to help himself while making your life miserable. I understand that you feel conflicted about maybe having some empathy due to the disability, but I would honestly remind yourself that his behavior and attitude certainly aren't conducive to improving the way people with disabilities are treated, and does no favors to other people with disabilities. Him having a disability (which I thought he refused to register for?) is not a free license to act however he wants and damn everybody else.

As for under or over reacting - does it make any difference in what you have to do? And either way, the situation is stressing you out a lot and I think that is legitimate.