I get that too. I'm have never gotten an answer for why. And stress and tension seem to take the blame for everything. But I think it just could be where an effected nerve lives and just gets some people.
Personally I would be the first volunteer to wear a bio suit and be hooked up to stuff and go about my day if only they could research the workings of migrane / fibro/ RA to find out why this happens to us !
Science fiction geek girl grandma mother and wife ,sister ,daughter , aunt, and friend . RA, FM, OA, eczema, slight asthma, depression , osteoporosis, and other things that I forget I have until they come knocking.
Live long and prosper ??
May the Force be with you. ??