I studied arts and psychology (not at the same time, however) and must say there are 'seriously psychologically instable' people in both groups...
Most of these don't manage to graduate, though.
I think a lot of fine arts-graduates are more happy because they took the chance to do something they really love. I remember from art school you really had to be motivated 100% to be able to graduate (a lot of hard work, handling critiques, etc.). Psychology was, as a different type of education, much easier. You just had to read the books and interpret and reproduce them. The internship was challenging, but also fun. With the arts study I had the feeling I was studying 24 hours a day, with psychology I could really take my mind off things (at least, during university time... working in the field is of course much more difficult).
Also, it's quite risky to study fine arts because (in the Netherlands) there are hardly jobs to find after such a study (being a teacher is most common). Becoming an independent artist is also quite hard over here.... the people who decide to go on and graduate in fine arts must know very well what they love to do, otherwise it would be a waste of time. Some studies appeal to many people who haven't got a clue what to do in their lives, fine arts is
not among those (in my country; law, economics, and yes, psychology are examples of this). These studies ensure a job (and economic safety), so people stick with it even though it's not really to their liking. I think this can make people very unhappy...