In fact, if you do a careful study of history, many of the best artists have "serious mental issues". The question is, how do we define "serious mental issues" and "art"? I don't think its a coincidence that people with off-the-charts creativity are mentally different than most other people. If your thought process is that far removed from others in regards to art ("creativity"), then it only stands to reason that your thought process would be very different from other people in other regards, too.