I saw a flash of checkers before my eyes!

Okay, so this is weird for me, but I want to know if it's happened to anyone else or if it's just a normal kinda thing to happen.

So I was in bed one night and was pretty much awake. The lights were off and I was looking out into the dark room. All of a sudden I heard this loud crack or something behind my head, near or even in my neck, and for the briefest of moments a flash of black and white checkers overtook my eyes. Little black and white squares all aligned towards the middle.

I was immediately freaked out "What the f...??" I said out loud. It wasn't like a small bit or a few spots in my eyes - all I could see for that one second was checkers. They were arranged in perspective towards the centre. It was like a weird screensaver. But it was real. I can assure you, I've never had this experience before and there were no checkers anywhere in the room!

So what happened?? Was it the matrix? Some strange vision? Am I mad? Optical screensaver/illusion thingy? The fact it was coupled with a loud sound was weird. I didn't feel anything and I knew it was strange. Hopefully I've explained everything. Is this normal??