What seems to have helped me is increasing my mestinon dosage. I am going to ask my neurologist if he can write even more. I find that overlapping my 60 mg every 4 hour dosages with 30 mg at 2 hours helps a lot. I only do this when I work and need the extra boost.

Exercising or even existing without it doesn't work.
Don't push yourself until you know what is going on. It is a pain and it is potentially dangerous. It is not your fault.