Ya know, I would just write down your limitations and how honoring them keeps you healthier and happier. Then I would describe how stressful it is for others to try to coax you to do what you know is unhealthy, and that stress can only add to your declining health.

Then provide the url for the national MS society so that if they really care about you and how to help you, they can take the time to learn about your disease.

Print it out, in multiple copies so you can hand it to people or keep it on word and e-mail it to those who need it.

I might imagine you are trying to put your best foot forward and look your best despite your illness. Its just no fun to have to explain this disease to people, multiple times.