I'm not saying the existence of a symptom (PEM) is as good as a diagnostic test; rather, in the absence of diagnostic tests, they are "enough" to diagnose CFS.

I'm not saying the existence of a symptom (PEM) is as good as a diagnostic test; rather, in the absence of diagnostic tests, they are "enough" to diagnose CFS. And PEM isn't the only common symptom, there are others, such as a constant lactic acid-like burning sensation in the limbs. I know you said you don't have CFS, but trust me - the fatigue we suffer after PEM is nothing like "normal" body fatigue after exercise. I think we'll find a diagnostic test eventually. At least, I hope we do.