For the game, I mean.
From what I remember from my psych textbooks it's important to distinguish between mood disorders, mental disorders, and personality disorders. If I recall correctly, mood disorders are the kind that require psychiatrists while personality disorders are behavioral in nature, but you can take some creative license here.
For example: if your behavior is consistently selfish/uncooperative, you can develop narcissistic personality disorder and must see a psychologist (branch of bureaucratic arts). If if you spend too much time in a small area, you can develop claustrophobia and/or depression and must see a psychiatrist for antidepressants. (psychology + a medicine skill, perhaps herbology + admixing).
Thoughts on this?
(edit) Since most of the opposed listed the "negative" aspect of psychological disorders as their reason for objecting, answer this: how would you feel about a psychological skill tree that only contributes and doesn't take away? For example, "focus pills" that increase your concentration? Or "mood pills" that act as a lighter version of No No Powder? Say the game doesn't add disorders proper, but adds a "Psychiatry" skill tree from the combination of Bureaucratic Arts, Meditation and Herbology. What are your thoughts on that?