Yeah I think I know the condition you're talking about. I don't often have any emotional response to things at all, not even on my last day of school. But then sometimes I get this tremendously exuberant feeling that rushes over me in a wave. I don't know what it is, I don't think it's bipolar or depression - but if you do think you do suffer from depression, then everyone says it's always best to get help. Personally I think art in all its forms is the most helpful thing, not perhaps for specific problems: there's nothing like Wagner or Wodehouse to broaden and better one's perspecitve on life, and reading T.S. Eliot always makes me re-evaluate the significance of my emotions, or lack of, and at the very least makes personal anguish pale in comparison to the overall agonized struggle of The Waste Land, for example.