So sorry this happened, this has happened several time to me by professors. I've been "called" out both private and publicly.

Please go into his office and tell him that his question shocked you into saying personal information that you did not want to share and his story really bothered you. Do not tell him your Dx'd or anything. If he asks why you were hospitalized tell him you were having a difficult time and you were hospitalized.

I honestly think that he meant it to be a conversation about the topic of the book cover you chose and has a negative opinion of the topic.