Welcome Bora -
I have severe fatigue too. My doctor evaluated me for sleep apnea - a fairly common problem in people with MG not sure about CMS. It may be that you aren't getting good sleep because of breathing issues and that would increase daytime fatigue. I do not have sleep apnea but for people that do there are several treatments.

My doctor prescribed Provigil. It is usually used for people with Narcolepsy but has been used with MS and MG to help reduce the fatigue. I think it has helped with my muscle fatigue too. Have you talked with your doctor about options for treatment? When I was on a lower dose of Mestinon my muscles got very tired quickly, had more spasms and cramps. Maybe you could talk to your doctor and tell them that you can't even get through the day anymore. Maybe you already have talked to them...Glad you found this place.
Gabe