Your story is similar to alot of us.

Sounds like MG to me, just because you fail that SFEMG don't mean anything, sorry. Your muscles are supposed to be warmed and exersied before this test is performed, and no mestinon for at least 24 hrs. You responded to mestinon and that means something. Where theres smoke theres fire................. so either your not making enough of the acetacholine for your muscles or something is blocking it from being used properly. You should also have had the Tensilon test. You have other autoimmune issues too, if ya have one likely you have two. Also just because you had one MRI for MS does not rule that our either, sometimes it can take along time to see plagues on your brain and sometime never, you also need your spinal cord MRI'ed.
Do you have crashes? Long period of weakness, that take weeks to get better.
You could have Chronic Fatigue Syndrom, that goes with sleep disorders and PLMD.
Bums me out when this diease can easly be dxed, you just need to find a dr who knows what the disease is all about. Like muscle weakness, they should see how many times a person can get off the floor, climb stairs, comb or brush your hair, these are all the things that make this disease a pain and also give it its name.
Anyways lois is right, burn yourself out good, go and walk, climb stairs.
I hope things go well for you tomorrow, take care, Patricia