Oh yes, barometric pressure definitely makes Myasthenia worse. I doubt they have done a study to prove this, but it does also impact other autoimmune disease such as MS and Lupus. I moved from an area with lots of barometric pressure changes (Seattle) to a place with none (San Diego) and I have noticed a huge improvement with my symptoms. However, the one storm of the year here just hit and I am miserable. I can't move any of my muscles and the Mestinon is almost completely worthless at this point. I hope you feel better!