For me, someone who was diagnosed with P.O.T.S., not "mild" P.O.TS, there are days that are worse than others & times that can be worse than others within that day.
There is a criteria for getting diagnosed with the syndrome. You either fit into the criteria or you don't. There are various forms of P.O.T.S. ,however , that have been identified in research & some faint who have P.O.T.S. while others, like me, don't faint in every day life (though they induced my fainting w/nitroglycerine on a tilt table).
I do think that some do suffer worse than others with P.O.T.S. if descriptions I've seen on medhelp are any indication. I think all with P.O.T.S. will find their lives altered by it... I know mine has been.
I agree, POTS is POTS. My son's heart rate sometimes only increases 25 or 28, which is below the 30 beats for diagnosis, while other times it is well over 30. While his tests results aren't necessarily extreme, he is debilitated daily by nausea. The symptoms don't always line up with his vitals.
So, I don't think the term 'Mild POTS' should be labeled based on test results and more so on daily symptoms and how it effects your life.