No, you are not being stupid.
I have changed to HGV two years ago now currently class 2 and I wasn’t happy in my last job. It was a dead-end job without any meaningful progress. When I got trained up for class 2 I did work my last job until I had a decent paid offer. It was agency work for NHS supply chain and guess what I still work there nowadays and still as an agency driver. In your case definitely won’t let 40K job go.
Apply for medical do the paperwork - get your provisional and find a place where you can have trial lesson-just to get a feel of the machine (it’s awesome)!! you can get trained up and get your licence while you keep your current job as at the end of the day it’s always useful. (also will take your mind away from current work-related issues)
Now moneywise class 2 you wouldn’t be anywhere near that money-unless you find the unicorn company 
in class 1 However can get very close to that after a few years if “correct” path chosen.
Lifestyle is obviously different - if you are comfortable with yourself and being on your own most of the time than its good start. Car drivers will hate you, the public will hate you if you are blocking their way etc…
As a lady you may find bit hard the state of some toilets never mind that some brakes you may have in lay by (guys just have it a bit easier)
Partner life may suffer if you get unlucky and find a place with long hours
and the list goes on and on.
I am sure that more qualified lads here will give you the proper look into this industry but you know what? I don’t hate it - it can be challenging at times but I like it that way (also time really flies). Your view from window will change every second and theres always something to do. When I finish my shift I go home with good feeling, I don’t have to bring any work related problems home with me (unless something happened obviously)
Think long and hard about the choices you want to make. Money isn’t everything but its important to have them. Think How hard you had to study and prepare for your exams… perhaps different NHS related work would make the difference?
I am not trying to discourage you at all Just try concider all options before you make your move