I was going to diff doctors with various complaints - lying down or walking my heart would start racing, standing up I’d get dizzy, nausea, etc.
I wore the Zio Holter monitor for a week.

I told my cardiologist and while lying on his exam table he checked my pressure - then I stood and he retook my pressure. Pressure should not immediate change more than 15 points and mine changed 30.
Dysautonomia/ POTS used to be uncommon but if you had Covid it’s more prevalent.
There is a tabletop tilt table test where you’re positioned in various manners but my doc diagnosed me without that test.

I’m about to start Fludrocortisone - I was hesitant bec I read you can’t have vaccines with it, but was told you can’t have LIVE vaccines and flu and Covid shots do not use live vaccines.
There are many interactions with other drugs so your doc might suggest other drugs depending on your current meds. I’m not suggesting you take this, but this is what I’m starting today.
I have ET and figure if I can get used to Hydrea I can handle almost anything!

See a cardiologist whose judgement you trust and have a list of all your meds and symptoms - you don’t want to forget something important.

I now have a pulse ox and blood pressure cuff. I once brought them to my doc’s office and checked my readings against the nurse’s readings on her machines to make sure they were accurate.

Good luck and remember you’re not crazy - you know your body best and can tell when something has changed. You might need to see several doctors till you have a diagnosis.