Dan, I was a bit surprised to read this and I hope you don't mind me saying something...
I don't work now but when I did it was in high pressure and high stress industries where it was all down to me and like you I used to obsess and stress and look at every scenario and possibility and have my response ready but despite it all I succeeded and I eventually learned the lesson that if I put the prep in and thought about
everything and planned for
every eventuality it helped and although it was a bit stressful I could do it and what's more I could be quietly confident that I could do it. There's that double edged sword thingy. The high pressure stuff then became almost just run of the mill. I suppose it was the mix of repetition over time and repeated successes that built up my confidence and eased the stress and anxiety and I'm quietly confident that you'll get there too. You may never get to the point that your heart rate doesn't quicken just a little when faced with a job because if you got to that point you'd probably be diagnosed as a psychopath
but I bet all the stress and anxiety eases a bit as you get into your stride. I'm sure it will.