Actually, I'm doing edits, not rewrites. I told my editor I'd have this novel back in to her by mid-month. I appreciate the deadlines; it means someone besides me cares whether or not the novel ever gets finished and polished.
I notice that my mood changes a lot while I work on edits. I can hit some real low points as I try to figure out how to fix what's wrong, and it's easy to get so down on myself and the novel that I just want to mail it off and wash my hands of it. It's a temptation I can't afford to give in to. People tell stories, and a lot of them are urban myth, about the novel they hated that turned into their bestseller. Writer's get depressed, or they get scared when they're digging deep and are outside their comfort zone, but the story I hear waaay more often is that it's the beloved novels that sell better. (Which isn't always the the same as selling well, but that's a separate issue.) The ones that you tune up to the very best of your ability and that you still manage to enjoy reading for the umpteen millionth time stand a better chance in the market. The novel that depresses you more often than not has something wrong with it, and you know it. Hence the depression.
So edits are as much about finding that emotional place as tuning up the novel. It isn't as simple as just cheering myself up, nor is it as simple as working out all the kinks in the plot. I find I have to work on both of these at the same time to get where I need to go emotionally, and get the novel where it needs to go structurally.