Please don't be ashamed. I will try this again, though once in the past few understood... but there's a big difference between shame and guilt and all that goes with them.
I don't see where you have anything to be ashamed about.
I can see why you might be disappointed in yourself, but really, I find no real cause for that either. (((Hugs)))
The thought didn't come from "nowhere." You have to know that. Maybe this is another piece of the puzzle of your healing, to find from where it came?
You are strong. Your past is part of you. Do you HAVE to remember it, in conscious memory? No, not in my opinion. It's there.. but perhaps in holographic form? I think "being healed" is a state when you no longer keep such past in conscious memory, but operate consistently from the past and in the present, newly each day. What do you think?