thank you all. great perspectives. that hr formula puts me in bed at 85 which means i shouldnt be up at all most days. i do want to trust my body and i realize that what i mean is i dont trust muself to read/notice my body's signals, and the key to this healing journey is going to be learning how to do that, so thank you for that, esther.
Main point:
My specialist advises using HR and BP as indicators for when I'm starting to stabilize after a PEM episode. Keeping a daily record of first morning (before getting out of bed) BP and HR gives you a baseline (your own "normal"). From there, you can judge progress in a PEM episode by comparing current BP and HR to baseline -- when you're back to baseline you can resume your previous "normal" activities. Otherwise, stick with lots of rest and extra fluids.
Extra babble not entirely necessary to the main point:

Since I'm currently in a PEM episode
and had gotten careless about taking BP and HR every morning (because it had been 6 months since I'd PEMed myself), I no longer have the baseline data that used to help me understand when I could safely increase my activity. I'm regretting that now. I'm having to go by how I feel, which is not a very good measure compared to BP and HR data. I always think I "feel better" before my body is really ready to go back to normal activities. We all want to think we can go by feel, but it's far too easy to want to do more, or to notice that we feel better than we were in the worst part of episode -- without understanding that feeling
better than the worst stage is not sufficient criteria when body systems are malfunctioning.
IMO, most of us are still in push-crash cycles in which we are in a constant state of (at least partial) PEM because we go by how we "feel" which has a lot of ambiguity, compared to using the data which has the benefit of being objective.
I didn't achieve long periods where I was not highly symptomatic until I was willing to take the data and manage my activity by it. That meant doing much, much, much less than I wanted to. I had to learn what my body's true limits were, not what I wanted them to be. It's a hard lesson, but not feeling like crap 100% of the time was a valuable reward.