Normally you cannot recall it. The brain takes several seconds to record what you are experiancing. Normally being "knocked out" takes place in a faction of a second so you don't remember it.
I was knocked unconscious a couple of times when I used to race motocross as a kid, when I ended up kicking away from the bike because I knew I was gonna eat it. I can only remember the start of the crash and flying through the air, never the impact with the ground itself.
I was nearly knocked out a few times when I took Karate as a kid. I was not very good at it so I got the crap kicked out of me often. Seems to me it was more of a black and white experiance - kinda like nitrosoxide at the dentist.
I suspect that website is probably someones attempt to receate a bad acid trip!
Wade.