Always nice to talk about creativity, rather than doing the hard work oneself. My friend is a genius in her work, not in her person (though she is pretty good there too). I think that there are all kinds of people who were creatively innovative and were mostly normal (Chekov seems to have been only ordinarly strange; James Joyce was mostly ordinary). But I think it is generally creditable that artists have a high incidence of mental instability, simply because the ability to balance the uprush of free creative stuff with the hard need to hammer it out into something coherently new is so rare. There is a great phrase: the mystic swims in what drowns the psychotic. True for artists too. If you can't shape the molten psychic material, you aren't an artist: you are mad. My Thought for today is an excellent example: this poem is only worthwhile because Holderlin was able to briefly hold his mind together -- but what makes it stunning is that you can feel the disintegration/integration as it goes along -- like a Van Gogh painting. It may be that the reason we are so attracted to the "mad tortured artist" model is that it makes the creative process overt -- we like the feel of the danger, as if we might go over too.
yours, Peter T.