When you're depressed, you can't remember what it's like to be happy. But when you're up, you can remember the depression, and when it lifts the relief is so intense that you'll do anything not to get back into that state. Of course, sometimes you don't have the choice, and it wasn't for a few years that I learned that there were things going on in my brain that were more complicated than I knew. The alien was still tapping at my window.