I totally understand your fear.
My job is very demanding, physically and mentally, but the physical part is killing me, so I decided yesterday to apply for a new job, an office job. I have no idea, if I even get a call for an interview, but I am already so scared. I scared of the interview ( I might sound like a total moran) and if I do get hired, am I going to be able to learn the new job, with major brainfog?
You are lucky to have an understanding boss, that is big points on your side.
I wish you all the best.
I may have been dealt a bad hand, but at least I'm still playing with a full deck. ( most of the time anyway).