Like Mestinon, Huperzine A increases acetylcholine. I'm not aware of that bring behind PEM.It can be very dangerous for ME/CFS patients to take corticosteroids daily at normal doses for extended periods. Very low doses are OK, but even low doses increase you risk of psychosis.
Do you know any ME/CFS patients who have found huperzine A and eliminated their PEM
I suspect PEM is much more related to oxidative and/or nitrosative stress. And/or insufficient BCAAs, particularly leucine and isoleucine.