I don't really have an answer to the why do we worry but I think with me it was a mixture or codependency but also being a decent human who feels for others when they're ill which clearly our A's are. I don't miss my former AH whatsoever but I do find myself now and then wondering how far down the spiral of disease he's headed and feel sad him for throwing his life away.
The mind racing and unable to sleep/be at ease sounds like anxiety to me and I wonder if seeing a therapist or even a doctor about it might help?
Just wanted to post and say you're not alone in what you're feeling.