If you have MG, you want to avoid ANYTHING that blocks acetylcholine from being transmitted. I would find something else to help with your pain - talk to your doctor to see if there is something else that you can take until you have a chance to see your neurologist.

You'll want to stay out of the heat and avoid too much strenuous exercise. If anyone gives you any grief, just ignore them - you know best what works for you, and nobody knows better than you how you are feeling. Give yourself permission to take it easy in order to conserve as much energy as possible.