That sucks but there are definitely other potential explanations. For example, ME/chronic fatigue syndrome can have similar symptoms to POTS, wouldn’t show on a tilt table, and is difficult to get diagnosed. I’m also not sure if forms of dysautonomia other than POTS would show. Have you had autoimmune testing? Other blood work? It is possible that it’s a FND/conversion disorder but I would advise against settling for that if there is testing you haven’t undergone yet.
have you done an echocardiogram stress test? my appointment with a cardiologist said that the tilt table test isn’t the greatest bc even people without POTS or dysautonomia will have symptoms of lightheadedness and BP fluctuations. it’s a game of ruling other shit out, essentially. don’t be afraid to go back and advocate for yourself. i’m lucky that i was a biology major and have a good understanding of human anatomy and its form & function. it helps me advocate for myself when alone.