I came to this forum in 2011 with exactly that issue, saying that I could not bring myself to shower, brush my teeth, etc., even though I was at that time not even depressed. Lots of people had the same troubles, and threads about it get started again and again, each acquiring lots of posts. And a shower taken is a victory - see that long thread in bipolar success stories.

It is so common that I wonder why it is not in the DSM.

I have not been able to get to the root of it, but I have been able to solve the problem in part. Wanna hear about my solution?