Question about POTS

Hi all you lovely people.

My nephew was diagnosed a while back with it and to be honest, i think it's a wrong diagnosis. But I could also be wrong on that, so wanted to ask a couple of questions.

First one, is pots a continuous condition? As in it doesnt just go away for a while then have a flare up for a day or two then go away again?

I ask cause lately i have seen some videos of people with POTS and i feel he has something different.

For instance, he worked for about 6 months doing hard labour and was fine. Had one flare up so was off for the day, but back to work the next. And then he went away on a holiday with his lovely gf and she mentioned he had a seizure while on the train. But that that is something that can happen? I was surprised no one did anything about it.

He no longer works because he had constant rib cage pain at the moment. Cant lift anything and his GP says that he has inflammation of the cartilage and tendons of the rib cage. Now thats been going on for about 9 months now.

Im very worried about him. And being the aunt, and that he is nearly 20, i cant exactly tell him what to do or to get a second opinion.