As I said, I have no idea of the specifics, but... You would likely have to involve somebody more than just your GP. You would have to show that J was fine for you, Y was not. And your employer would have the option to reassign you to another role, with similar (but not identical) responsibilities (or retrain you) and similar compensation. I am neither a lawyer nor an HR specialist, but that is to the best of my knowledge the situation. In the specific case I know of, the employee simply opted to stop flying for work (we offered him a local role). As I said though, the health danger was very significant--life or death--and there was ample evidence that it was an urgent problem--he almost died on a flight. How significant back pain is, whether you incurred your injury during the course of your work duties, etc. all probably matter. Talk to your company's health and wellness manager if you are serious.