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I've worked in some offices which had horrendous ventilation and no ability to open the window.

I don't care much for ventilation systems in general ... never really works all that well, and are vastly inferior to just opening a window. Some are noisy, too.

Sick building syndrome?

https://en.wikipedia.org/wiki/Sick_building_syndrome

It wasn't a great work environment lots of big fish in little ponds.

I suspect the "every day" part was not accurate and it was just headaches they were getting not migraines. But a migraine meant they were sent home (no pay) a headache wouldn't allow that although I do know they truly believed they were migraines.