Mine was kind of the opposite to yours - even gentle exercise would aggravate myasthenic weakness and it did not help to build stamina (no drugs at the time also) Maybe that depends on what stage of a disease process you are at. Gentle exercise is good lately (....finally!)

Quite a few years ago I also had severe, heavy velvet curtain brain fog hanging over me for 2 years. Absolutely the worst thing is constantly not knowing if you are stuck with it for life or not. Mine went away completely without help from any changes in my psychological well being whatsoever! Which actually shocked me into a realization that doctors can be SO wrong!
In my country the last thing I read was that they have run out of funds for promising results using Ritubmax for M.E. patients who are found stashed away in dark bedrooms 24 hours a day feeling that to sit up in their beds is tantamount to having run a marathon......

Itīs a long lonely and scary journey doing it all on your own.

I made it....So there is hope

Anacrusis