I experience low-grade depression like MM said, too. The only thing I can add is that I get the chills every night when i am depressed (low-grade or severe). I don't usually get chills during the day, but the second the sun goes down, ugh... I also tend to think I am overwhelmed and there is no way out from under a heap of responsibility, which just adds to my down-mood sometimes.

Side note...I haven't been depressed in more than a year and a half now and I have slipped into low-grade depression. It sounds weird, but it almost feels like an old friend right now. I don't want my "friend" to stay very long like it usually does, but nonetheless there is a very nostalgic feeling that I am experiencing this time. I haven't felt that before.