Temporary Blindness?

It only happens when I'm really, really hungry, or when I'm in pain. The most recent time it happened was when I hit my funny bone and it started with dizziness. Then I went blind in both eyes. It works like: A load of black spots eventually take over my entire line of vision. I usually have to close my eyes, otherwise it will make my eyes hurt really bad. When it lightens up, everything is yellow for about a minute. Then, as it goes away, everything looks static-y. Then, I can see just fine but I'm left somewhat weak and dizzy for a few minutes. What is this?