I have experienced a lot of those cycling self-destructive thoughts. When depressed, I really beat myself up for having no reason to be depressed, etc.. But then, when I'm out of the depression, I realize that that was the depression talking. What a relief to come out of it and know that it wasn't my fault at all.

I would suggest seeing a psychiatrist, because what you're going through sounds like symptoms that could be helped with medication. I hope you find relief from this depression monster soon (it really is a monster!).