I've been treated by a doctor of Traditional Chinese Medicine on and off since Nov. of last year and we've narrowed down some herbs that are quite helpful for me. They are tablets widely available online (especially UK) that are the first and only thing that affects my PEM/unbearable hangover feeling. The tablets are called Xinhuang Pian. Apparently it is generally used for arthritis and acute viral infection. I found the main ingredient alone, pseudoginseng, to be somewhat effective but not as potent as the combination in the patent formula Xinhuang Pian (I tried pseudoginseng alone because it's cheaper). It seems to work for PEM the way aspirin or tylenol works for a headache. The PEM is just gone for a few hours and then I take two more when I start to notice it again. I've had no side effects. Hopefully someone else finds it helpful. BTW, I took care of A LOT of other layers of this disease before reaching the point where PEM was my only significant symptom. I don't know if it would be effective for other aspects of ME/CFS.