If mestinon helps it's a pretty good indicator even if all tests come back as normal it does not mean you are not a myasthenic many people have only a clinical diagnosis.

Not wishing to frighten you but I do not think it is a good idea to choke down anything if you are having extreme swallowing difficulty it may be best to concentrate on liquidized food until things stabilize, and even that with caution I have choked on my own saliva in the past.