POTS disappears at night sometimes? Also same thing with IV saline?

I have seen others post similar. I find it really strange at night sometimes my sitting HR can be 55-60 and standing will go up to say 90 then quickly fall back down to 65 (and stay there). I do have a milder presentation of POTS to most but I find it confusing. I also have GI issues (gastroparesis) and that part rarely seem to let up but the POTS heart rate really seems to change day to day.

Anyone else experience similar?

I also had an IV saline the other day and for the next 2 hours my standing heart rate was in the low/mid 60s. Then I ate a cheeseburger and it spiked and stayed higher for the next 2-3 hours.

I believe I’ve got neuropathic POTS (blood pooling and no real change of BP when standing) and I’ve read multiple times it’s due to verge damage. But if my HR can still sometimes be ‘normal’ I don’t understand how it can be nerve damage? Then sometimes people refer to it as ‘dysfunction’ rather than damage. Seems like a lot of conjecture about what is actually happening to the ANS.