Has anyone ever rolled their eyes too far back in their head?

It may be hard to believe but I have. If you consider your eyes to sit on a 360 degree axis, 0 degree being looking forward, I have rolled mine back to about 140 degrees, I was tripping and I was laying on my back looking up and following a trail of imaginary lines. As I continued to look up and up, without my noticing I began looking into the back of my head, at the bottom of my field of vision I saw this bright white light coming up over the horizon, as I looked up more the light came out more until I was looking at a circle of light brightwr than any I had ever seen, it also burned my retina more than anything else ever has, it freaked me out and I bolted upright and actually felt my eyes flip back around facing forward, it felt like they did a full 180. I had an after image burned into my vision for hours, even now as I think about it my eyes begin to burn, and the really crazy thing is that my friend did the same exact thing, and when he told me about it I had no idea what the hell he was talking about, a year later I randomly did it on my own. What was that light? How did it burn my retina so badly?