@Barry53 @Aurator I'm inclined to think this is a question of semantics but that it's a question of science as well - you have to pick the correct words to use but, in a scientific context, you have to be clear about how those words are defined and words like tiredness and fatigue are thrown around with abandon (being tired=being terribly busy=some weird sort of status symbol) and mean different things to different people. Typing this really rams it home into my frazzled brain just how inadequate a term 'chronic fatigue syndrome' is..
Clarity and agreed definitions seem especially important with ME, since the whole thing is currently bedevilled by a lack of consistent diagnostic criteria, (never mind the absence of a biomarker.) I'm sure ME is both under-diagnosed and over-diagnosed for all sorts of reasons, but I can't help thinking this lack of clear, consistently applied criteria is fundamental. How can you get the diagnosis right when it's not clear what is being diagnosed? And of course the whole picture is muddied by the existence of different sub-types plus all those people who are given the ME/CFS label but in fact have another condition altogether and also the manipulation of facts in the service of vested interests..........
I certainly agree that the 'fatigue' that comes with ME is very different from normal tiredness - and PEM is in another league again. I'm still faintly astonished when people say something along the lines of 'I get really tired too - I wonder if I've got ME?'

Fatigue seems such an inadequate word in the face of such a devastating condition.
Excuse my rambling - I'm no scientist - but as an erstwhile lawyer, I do take a strong interest in how things are expressed, definitions, avoidance of ambiguity etc..