Someone with POTS will not be able to maintain the blood pressure while standing without a high increase in heart rate. Heart rate will sometimes increase a lot some seconds after standing up, both caused by a drop in the blood pressure, and the fact that muscle work with standing up (especially after sitting for a while) requires an increased heart rate.
It doesn't sound like you have POTS if your heart rate normalizes shortly after standing :) but of course a physician should have the last word.