I think it's safe to say that transmogrification magic in general doesn't have any significant effect on the mind in that "universe".

Of course, our only examples of people under the effect of long-term transformations are people who were crazy to begin with (Barty Jr., Wormtail, Voldemort), and it's safe to say the experience didn't make any of them saner.

(Although, in the case of Barty Jr., the guy he was transforming into wasn't exactly a paragon of mental stability, either.)