J, A couple things u said are right on target for me.

"The trouble is that the less I accomplish, the less I feel about myself. Add to that, I've been incredibly forgetful."
"It's one of those downward spiral things: I feel lousy because I'm not performing as well as I think I should. So I don't perform as well as I think I should. So I feel less able to deal, so I don't perform as well.... you get the idea."
"I doubt things are truly as bad as I feel like they are, but it is a difficult feeling to shake."

Its like u wrote eactly how I feel. I have not been able to post about those feelings. I feel bad about it. Guilty. Ashamed of myself for not doing what I know I can do , But still dont. Im, still mad at myself for still being affected by my past. I cant seem to get over "IT", or the left-over feelings. The self-doubt & fear-of-failure are like a Re-accuring illness. One that cycles in & out of my life every couple weeks. The "lows" r extreamly low, the "highs" r just OK.
Thanks for sharing ur post & helping put things into words.