mellan, If I were you, I would go see a pulmonologist and have breathing tests done to make absolutely sure how your chest wall muscles are!
Atmospheric pressure does effect a lot of things. And there are some who say that our atmosphere is shrinking, bringing clouds even lower. Here is a good explanation of what can happen when pressure changes.
http://psychcentral.com/blog/archive...orm-is-coming/
Jana, MSG in foods, like tomatoes, can cause a migraine for me. Thankfully, I haven't had but one or two in decades. When I do now, I only get the scotoma and not a headache. Though I do feel sort of yucky for several hours.
mellan, please make sure that it's not a case of MG worsening - whatever the reason.
Annie