I can only answer for myself, but it was part of rolling PEM that I didn't even know I was experiencing.
Partly because PEM wasn't really known about back then, but even when I cottoned onto the idea it took me far too long to make sense of it. The trouble was that it involved acknowledging I was doing too much, and I didn't want to know that.
One of the reasons I didn't realise the extent to which PEM can be an ongoing thing was because the symptoms fluctuated. I felt okay some of the time. I only recognised what not being in PEM felt like when I finished work. It was already a massive life change—I'd worked for decades—so I decided to stop everything except basic daily living activities and low-key social stuff for a year. Then I got it.
Obviously I can't know whether or not it's the same for you. But for me, some of what you describe is the result of over-activity.
		
		
	 
Wow. A lot of things click into place for me here. 
When I first called in sick (5 years ago), I was in really bad shape and 'diagnosed' as having a burnout. I stayed home for 2 months, and then slowly went back to work, but have been ill since (still worked full time with hardly any sleep, thick brain fog, severe anxiety and fatigue, and feeling as if my brain was a brick). No one noticed anything, I was still a high performer (how is beyond me).
Then, when I called in sick again, there were about 6 months of insomnia, severe anxiety, brain fog, and fatigue, yet unable to rest/relax. My body started to calm a bit after these 6 months. I have slowly improved over time, not without hickups, but still, some very slow improvement (mostly spending in State 2a).
@Kitty, you wrote "The trouble was that it involved acknowledging I was doing too much, and I didn't want to know that."
This is where I'm at now. Based on your comments, I start to realise that I need to be do even less to stay in State 1. I should avoid 2a as much as possible and try to not move to 2b. The fact that 2a might be PEM already, is a big aha. 
Don't worry about 'derailing' the conversation, everyone. I'm learning what needs to be learned, although I definitely don't like the idea of doing even less.