Hi...have they ruled out MCD ( mast cell disease) ? EDSers are prone to over produce histamines and it can play a role in symptom flare ups due to weather,,,,,,
I have a rough time with not only big weather pattern changes but seasonal ones as well....I try to avoid things I know will make my flare ups worse....I do have EDS and tethered cord in addition to Chiari.....but I do not have POTS and I can not offer insight on what to look at there....so do talk with your Drs.
Hope you begin to feel better soon so you can enjoy the holidays.