Yes! This appears true. Not all despair fits into this model (some people fail to get the upswings), but I think a large fraction does. There's one important, non-obvious corollary: not only should you not resist the slide into despair or try to never have it, but you should optimize what you do in that time! If, for example, you respond to the feeling of despair by drinking alcohol, you'll probably never get to have the thoughts that mood had to offer.