Heart rate and temperature variability causes?

I'm not sure I have too much to offer here, but I definitely have monitored my heart rate closely due to a long history of POTS. My heart rate when I have been very ill was about 75 BPM lying down, 90 sitting upright, 110 standing, 120 walking around, and exerting myself was impossible. As my overall condition improved, and I learned how to manage my POTS better through proper hydration and salt intake, my resting heart rate has gotten lower (60s, both lying and sitting). In the morning or other times that I'm somewhat dehydrated, my heart rate still climbs above 100 when I'm standing up and moving around sometimes, but I don't have any symptoms from it or notice it unless I take my pulse. I'm also able to go for walks and easy hikes, do yoga, and do strenuous yard work much of the time without POTS symptoms.

I also have experienced flares of POTS symptoms due to lower blood pressure when I have been taking lemon balm (which lowers BP, which for me is always on the low end, like 90/60) and when the barometric pressure drops precipitously.

If I am nervous about something, even just a little bit, then my heart rate is faster. (I know this is normal, but I point it out just because people often only check their stats in a medical context, when they might be nervous.) I think it's good practice to keep my pulse oximeter with me and try to breathe my heart rate down when I feel stressed.

After taking Alka-Seltzer Gold several times in one day to combat a herx, I threw my electrolytes way off and ended up admitted to the hospital because my heart rate would not come down from the 150s, even lying down. It gradually normalized but was freaky.

I notice that my pulse ox is 98 when I'm compressing my ribcage by lounging on the couch, 97 when lying in bed, and 99 the rest of the time.

That's interesting on the Alka-Seltzer gold I wonder what was going on there. I'm assuming that if you have a low or pulse that might be a good indication of a lower level of inflammation. All that micro circulation infection causes the heart to have to work much harder.

What I don't know is if the oximeter is able to distinguish the difference between all of the different gases because I'm sometimes suspicious that I can be so air hungry but still have 99% saturation is it picking up carbon dioxide or hydrogen?

Running wild sometimes I'm suspicious on whether there's a difference or not. Seems like most of these bacterium are just vectors for viruses and fungus.

pulse oximeters work by measuring the colour change in haemoglobin in your red blood cells caused by the amount of oxygen they are carrying by measuring the differential absorption of red and infra red light

other gasses do not change the colour of haemoglobin significantly - so do not affect the pulse oximeter readings - this is why they use this mechanism as the basis for the oximeter

long covid patients also have air hunger or shortness of breath without a measurable drop in blood oxygen saturation - suggesting other mechanisms are at work in these chronic conditions.

for me some was the hpa axis and the heart just regulating the blood flow by increasing bpm as bp would drop out . the other part was actually the spasms of adrenal glands releasing surges for almost no good reasons except lack of magnesium and nerve degeneration. i figured it out when i was awakened quite a few mornings with the racing heart , ready to fight or flight.
nitric oxide and licorice helped bp during treatment but adrenal spasms didnt stop til bart was addressed. and rest and vitamin c was the only fix . hope this helps someone somewhat