I think it's possible to be depressed when everything's going well and happy when everything's going wrong. Emotions stem from internal circumstances rather than external. It could be a physiologic response, or maybe there's something in your past that you've never really dealt with head on that's bringing you down now. Sometimes there are even things that have been blocked out by the mind because they were too painful to deal with and are now coming to light. I don't know the particulars of your situation, but if this goes on, you may want to see a therapist/doctor. Do you have any spiritual beliefs? If so, that may be helpful too.