As far as being too "smart" for a position, I would prefer to look at it as not having a position that engulfs my life. I am happy in my career and though it doesn't flex my brain very often, I enjoy it, and even if I'm not 100% there are parts of my job that I can still do. Most importantly when I'm done work I'm not exhausted and still can have my life outside of work. I have had the other type of career and I'd rather have my life outside of work.

As far as being too cautious, this could be a self esteem issue. It also could be a control issue. Perhaps you aren't stretching yourself out of fear of the unknown? I struggle with trying to control things, and this has held me back in some aspects of my life. Mostly in not being in the moment and enjoying myself completely. My therapist has helped me with that. Do you see a therapist?

Ruminating over what you see as a "Mistake" can be a function of the illness or it can just be a habit. I struggle with this too and it never has a positive outcome. When I start to do this I say "STOP" in my mind to break the cycle.