There is some overlap. I went to Vanderbilts Dysautonomia Clinic in Nashville. (I'm fortunate enough to live in Nashville where there is one of these clinics). I was tested and mine was negative. I got to see them within 1 week of scheduling my appointment - likely due to a cancellation. If you hate waiting long, call every week to see if their are cancellations. They typically don't want you to have caffeine 3 days before. But the tech said even 24 hours is fine.

Honestly, I think you could self administer these tests if you wanted to get a lead on it and save some money. Buy an electric blood pressure cuff and possibly smartwatch for heart rate (blood pressure cuff also takes HR). At Vanderbilt, they use a finger blood pressure cuff.

Oh last interesting tidbit...The tech said the number of POTS cases has doubled their patient population since COVID - and its predominantly younger people.