I am collecting my new car on Friday after a 14 month ordeal left me without one and naturally I can't do anything else until Friday now as I'm seemingly paralysed.

I need to do little warmups to get started on things, little distractions. A little puzzle, a walk. If you need to do something NOW, go hold some ice for 30 seconds then start immediately. You need to distract your central nervous system to get it out of the loop. Physical sensations or activity works best.