I prescribe a dose of Woody Allen's "Annie Hall" for the link between being a funny person and being depressed at the same time. I've seen it at least ten times (since the late 70's to just recently), and always find something new and relevant in it. (Apologies if you've already seen it. I was amazed to find out there were people who hadn't seen THE GODFATHER, so I don't assume anything anymore!)

There was also a Canadian documentary few years ago on Curmudgeons - people who raise being irritable to an art form. see tvo.org or search cbc.tv

Just the act of writing (and reading) on PC elevates my mood, although it doesn't do much for my motivation...

You sound about right for an artist to me, though! Feelings out onto the paper, you have a way. Have you looked into books or classes on art therapy? An ED type class I took had us draw a little and I was quite surprised at what came out about how I felt about myself.