I was with a guy who went through this same thing. we were downhill mountain biking in fernie, BC in 08 and he crashed pretty bad, basically went heat first into a tree I think... he was no beginner either. I turned the corner and he was laying on the ground, I laughed and thought "im leading now fucker"... except he didnt get up or answer back. I went up to him and there he was, blood pouring from his ears. he was asking where we were, what happened to him, what day it was etc... 30 mins later on the way down the hill to the ambulance, he couldnt remember if he was married (yes) if he had kids (3) what he had for breakfast. he kept asking me "where are we?" it was scary. he lost his balance for a year and sense of smell and taste for 3-5 years. not to mention the bones he broke in his face... he came very close to dying that day in my arms on a mountain, as other bikers flew past us, ill never forget it.
same thing as the video and its what it really reminded me of and they way he was acting, he probably had some serious head trauma or med drugs.