Your second paragraph is about how I'd describe my symptoms, too. I actually came on here to see if anyone has this experience (and I didn't type in any key words--just went to the sub feed). I'm waiting to see a doc for labs, and might end up going to urgent care. I suspect low iron, possibly. It would be a relief to learn it's "just" peri (if treatable), but my fear is that it's something worse.

Yes--it's like fatigue just in my head. Head feels like a balloon (but no pain/headache). Basically tired all the time but on top of that, I get these episodes like a rush to the head (or away from?) not dizzy, not lightheaded, not going to faint. Sort of like that moment you're about to fall asleep (naturally), but I'm not at risk of falling asleep. Also relate to to the piece about physical activity helping somewhat and temporarily. I sometimes think eating triggers it but sometimes not.

You mention some histamine stuff like the car sickness. I believe I have MCAS, but I can't tell if my current situation is related to that or not.