I've suffered from moodswings since I was 15. I get depressed for no conceivable reason. I feel depressed and frustrated and angry and I almost always hole up and try to take a break from the world. If I write, it's not very articulate and extremely whingy and usually only serves to fuel my own frustration with the situation.

I'm tired. I'm frustrated. I'm angry. I'm depressed.

I can't tell you how often I feel that way, even though my life is good and I have nothing too serious to worry or complain about.
Frustrating as hell, and probably the reason I don't often write when I'm in that headspace.