I dont know what disorder he has but taking any kind of medication makes my anxiety go through the roof so I can relate.
As for what to do, it sounds like he needs to learn to trust himself and be sure that he is ok.
My biggest problem is I always find myself negative talking and telling myself that I am going crazy or that I am losing it or whatever, and Ive actually convinced myself of it sometimes.
I am going to really try and not do this, as well as try and up my confidence levels and my place in the world and with myself and I bet my anxiety will vanish.