Hi rach,
First of all I have to say WOW 4 times you've had these tests done!!! I can't imagine. I can share my own experience with you. I had both the nerve conduction and single fiber test done about 6 weeks ago. At the time I wasn't on any medication for MG. I had my test done at 3:00 in the afternoon so I was wore out before I ever got there. I am a smoker and a coffe drinker and had both before the test and still had good readings. If I remember right they said they wanted to get at least 3 good readings and they did. You may have already addressed this and I didn't see it. I am in a bit of a fog today but have your other EMG's come back positive for MG? I agree stopping the Mestinon a couple of days before would probably be good. Since it is so short lived I would think 2 days would be plenty of time to get it out of your system. I wish you luck!!!
Take care,
Kendra