I'm sensitive to MSG but only in unusually large amounts, so it usually doesn't bother me. If there's enough in a food to make me really thirsty soon after eating, that's too much and is getting into the neighborhood of migraine trigger.
I really wish it was just not used. It seems a rather useless ingredient, and difficult to avoid if you eat out or eat any convenience foods - which I can't afford right now anyway, so I guess that's one advantage of being broke. I cook all my food and know what's in it. But it's even in canned soup, and condiments. There are so many people sensitive to it, I don't understand the thinking behind that. It's like whey, my spouse has to avoid dairy (due to allergy, not lactose intolerance), and whey or casein are included in the most surprising things, usually not necessary at all.
If I have a meltdown of any degree I usually wind up with a migraine the following day. Definitely stress and especially anger/frustration related.
But mine can also be triggered by weather changes and other things, so for any given migraine there are sometimes two or more possible triggers going on, some unavoidable.