As
@Bra****
mentioned a medical extension is not easy to obtain. Physically not being able to fly is quite different to “it’s difficult for me to fly”. With a broken leg, or a broken arm for example they’re not gonna let that one pass. Being in a hospital on a ventilator or such then that could well be a reason to issue one.
The pure fact that it’s difficult for you to travel has no bearing on the fact the you “can’t” travel.