Welcome sarahbear!

I am technically still a mystery, but LEMS and MG are high on the list.. I get IVIG for whatever this is.. I have many of the symptoms, especially of LEMS it seems.. but I do have confirmed Small fiber neuropathy and have had tachycardia since this all began with hypotension, however i guess for whatever reason the Tilt table test wasnt' officially positive for POTS.. which is odd, as I got very lightheaded and my heart rate went up to 164! can't remember what my BP was though.. My eyes showed autonomic involvment as well. Sjogrens has also been proposed..

Sounds like you definitely need some sort of treatment asap! I only do IVIG and it works really well most of the time.. I also have the elephant sitting on my chest thing swhen symptoms get worse, it's not fun at all!!! Good luck!