I hope that you are tired of your job or tired of this kind of thinking....if that's what's wrong, is it feasible to leave the job you have for something else you'd feel better doing? I know the job market sucks.

There is a possibility there's something physiologically wrong. I hope that there isn't! Are you forgetting things you used to remember easily? Do you feel disoriented sometimes? I just read Still Alice, by Lisa Genova, which is about Alzheimer's, so this is on my mind.