Hi Smirleygirl
Welcome to NeuroTalk

.
Elevated levels of anti-AChR antibodies are usually strongly diagnostic of MG.
However elevated levels of these antibodies can also occur in people with Lambert Eaton Syndrome; this is a "false-positive" result as far as diagnosis of MG is concerned. These antibodies are not associated with POTS.
Maybe this is what applies to you.
Best wishes.