That is a tough situation...

If you don't feel comfortable disclosing it, it is your right. My thoughts is he will probably figure it out eventually being a psychiatrist and all. The thing is, he is not your personal doctor so I don't think he has the right to pry. A good general answer would be your not feeling up to par and end it with that. If he continues to ask questions, you have the right to tell him it is personal. Idk, it is going to come down to what you want and feel comfortable with. Sorry if I didn't help.