Every time I go through something stressful, like finishing a project and showing it to people, or preparing for a very important interview, I succeed and it's done and over with, and then depression gently slips in and then knocks me out unconscious over the next few days, and I can't do anything but lay around and feel depressed/almost suicidal for the next few days. That's not normal, is it? Why can't I just relax after a big event without being so negative about it?