I’m sorry to hear you’ve started a relapse.
I’ve unknowingly flown with a relapse (I wasn’t diagnosed at the time).
I didn’t feel particularly well on holiday, but assumed it was just a combination of lugging a heavy case around, and wearing some new boots I hadn’t broken in properly (I had particularly bad problems with my feet).
I’d only been back a few days, when I was up at the doctor’s complaining it was painful to walk, and I feared I might have broken a small bone. Was seen by a locum, and sent home with no treatment and a ticking-off, as: “That is impossible, unless you are very athletic or have a gait problem”.
I mumbled something about: “Think I do have a gait problem…”, but got short shrift.
Roll on another few days, and I’ve now lost all sensation in my feet, and back up at the doctor’s again - referred straight to a neurosurgeon this time, for suspected slipped disc.
Anyway, long and the short, it was MS - and I’d unknowingly travelled at the start of a relapse (wouldn’t have had any choice if I did know). All my theories about “new shoes”, and “strained something lifting the luggage” were complete codswallop, and I’d been relapsing (as I now know).
As far as I know, there is absolutely no special danger associated with flying with a relapse. Inconvenience, for sure, as it’s not a good state to be travelling in, but it’s not dangerous.
You should NOT sit next to an emergency exit if you have any known physical disability that may impede your ability to open the door, and so obstruct the escape of yourself and others. Certainly, in the U.S (probably other places as well), I believe it is the law you must declare it if you have any reason to believe you might struggle to open the door, and you will then not be permitted to sit in that seat. Other than that, I don’t think there are any issues with flying, though obviously there may be practical considerations - for example if you have any form of incontinence.