Hello Lucy and anyone else reading this,
I have spoken with TEFL instructors and they know of others with chronic conditions who work abroad. They are reasonably optimistic that only a minority of countries will bar someone from a work visa for such a reason, those likely being middle-eastern nations. Therefore, I am moving forward with my goals and will begin working towards my CELTA in a few weeks. Thank you for your vote of confidence.
As far as MS itself; and in my case the most common and (fortunately) mild type, known as relapsing-remitting multiple sclerosis; the treatments have become, and are yet becoming even more so, affordable and accessible throughout the world. When diagnosed, this was the most difficult aspect to swallow, that my dreams of living internationally might be put to rest. This fear still occasionally raises its head, as it did a a few days ago. But it appears as if this will only be an occasional inconvenience to my life.