I used to have regular migraines starting a few years ago. However, after I took up cycling they became less regular, and I haven't had one since about this time last year.
I would get flashy lights in my eyes, and they would spread until I was almost completely blind. (I still feel ill even thinking about those flashy lights!)
After about 20 minutes they would fade away, and then I would have a really bad headache, and I would avoid lights and sounds at all costs.
I'm not 100% sure on what causes them, but luckily I found a cure

I down as much water as I can, then eat something really sugary, then I go to sleep, and wake up feeling fine

(normally after sleeping off a migraine I would feel like crap for the rest of the day, and the day after)