If you haven't experienced a migraine, you don't really get it. It's hard to describe - like being hung over without having had anything to drink, like your brain just tops fitting in your head. Pressure builds up behind your eyes, and light and noise make you want to punch something, only you can't move. Then your eyesight goes - first a little blur that makes it difficult to read, it slowly builds until you can't see anything, and trying to focus your vision only makes the headache worse.
It is horrible. I had one of the worst migraines of my life today. I need to go to sleep now.