Horrible things. I've only ever had three, first time it was caused by driving into the sun with telegraph poles in front of it causing a sort of strobe effect, next one was working in a dark pub, I had to focus on a fairly delicate job, there was a window directly above what I was working on and the sun was streaming through it. That was in Shirley precint. I was in such a state by the time I finished, a copper saw me stagger out of the pub and towards my car hahahaa, he came over and asked if I planned to drive while clearly drunk. Explained the situation, he sat me down on a bench and went into the pub to check my story, then came back and grabbed a taxi for me, said to come back for my car tomorrow. Top bloke that.