I can totally relate to what you've said, Wiz.
Some days I can do more than I normally would do in one day. Some days I'm doing good just to get up and get showered.
My son made a comment one day about the treadmill in my room. He commented that he had moved it for me and wondered if I was "ever going to use it". That struck me wrong. I told him (rather sternly) that I use the treadmill when I have the energy to......otherwise I let it sit. I told him I didn't realize he was keeping track of when I did or did not use it. I think he got the message......
I get so tired of explaining (or trying to explain) fatigue to people. And I get so tired of rude people who want to tell me that if I just got moving I'd feel better.

Next person that says that to me......I'm gonna ask them where they got their medical degree from.