On the contrary, I'd argue that migraines are probably much more common than diagnosed, rather than the other way around. Migraines, much like seizures, vary in both symptoms and severity.
Basically, a migraine is a “day-ending” event. In my case, I’m fortunate that I can still get stuff done in the morning, but after lunch, the day’s pretty much a write-off.
I’m really grateful that they are so rare (I’ve had three full-term, and one “aborted” one, in the last 30 years). My mother used to get one or two a month, and her day ended fairly early. When I was a teenager, I got them more frequently.