I think I can safely say that I am a mestinon pysridostagmine responder. Current dose is 30 mg 3x per day, but I have been prescribed up to 60 mg 3x per day. I haven't tried the higher dose yet. But I did find at one time that the lower dose ceased working so well. Was originally prescribed it for POTS, but have found that it helped with other symptoms as well, including cognitive dysfunction, dry eyes, constipation, etc.
I have not found improvement in a key symptom, which is non-restorative sleep. It is still the holy grail for me. Without restorative sleep, nothing works in any consistent fashion. I am back to being a vegetable. Probably in the 20-30% range. I use the Dr. Bell scale in terms of severity.
I do have at times, the muscle cramps, which are a pain, also stomach pain, but this is intermittent. I can't believe I am actually able to spell at times. Though I still have to heavily edit everything I write. So forget about the spelling part!
For POTS, I like ivabradine - but most of all IV saline infusions. But travelling to a hospital or infusion room makes the IV saline nearly impossible.
No improvement in PEM/PENE. My symptoms have not been digestive/ gastro symptoms. I have always been mainly in the cognitive dysfunction category - and of course the lousy or non-existent sleep.