Wtf was this?

From age 12-21 I got this recurring thing where I would lose half my vision. I don't mean that I would lose vision in one eye. I mean half my vision in both eyes would disappear. It would happen once every couple months and start out as this pulsating rainbow in my left field. That rainbow would grow until the center was big enough to be blank, and it would keep growing until... yeah, half my vision was gone.

I don't remember the first time it happened. But I remember the last time. I was old enough to be driving myself. I was in the parking lot of a store, ready to leave. But it started. I got freaked out and called my parents. My mom and some of my siblings showed up and we just went shopping in the store for awhile while I held onto my mom like a blind person. After an hour or two, it went away and I was able to part from them and drive home.

But I've never heard anyone else describe anything like that before.