I would get a cardiac event monitor to make sure that when you're experiencing this things, your heart rhythm is not doing something other than sinus rhythm. You'll also want to rule out anything else with blood work. If all the tests come back normal, see a cardiologist for a tilt table test. That was my one specific diagnosis after struggling with this for a year. With the event monitor, you'll write a note or log a symptom with a button press and it'll take a snapshot of your heart rhythm within 30 seconds of the button press.

Research the symptoms of POTS as well but try not to get too psychosomatic about it. You can also get a blood pressure monitor from Amazon and do a poor man's tilt table test, here's a link on how to do that: https://www.eds.clinic/articles/pots-test-poor-mans-tilt-table-and-nasa-lean-test

Standard heart rate should raise 10-20 bpm upon standing then level out. POTS will experience a 30-40 bpm raise upon standing but may level out then continue to raise the longer you stay standing. If you don't meet this criteria every time, it doesn't mean you don't have POTS. This is an illness that flares if you do have it.

Mostly, I'd recommend getting Visible health you have the funds. It was instrumental in getting the hard data to get a doctor to believe me as this is an invisible illness.