POTS

  What exactly  is POTS and how does one get diagnosed for that?  I wonder because my sister has that. She had a PFO closure, but didn't feel to good. She said she kept feeling like all of a sudden she would feel like a pulling from inside her head and would feel very bad, two months after her closure her dr. advised her to get a tilt test and there is where they found her to be positive. She was never able to take plavix.  I have been feeling that way or maybe like a fainiting feeling, but I dont faint, very weird and she suggested I tell my dr. about her and her test. She suggests I have a tilt test. I am just worried that it is just the plavix making me feel this way.  Anyone else have these strange sypmtoms after a pfo closure?