So, who out there was complaining about the "don't lead with your head" crusade? Where are you now?
Anyway....
I don't believe this looks like a serious injury. What we're likely looking at would be a nerve compression, POSSIBLE spinal cord compression (which would disrupt motor nerve function to the extremities, but would not result in permanent or even long-term paralysis), or being knocked out. Given that Xavier gave a somewhat spaghetti-armed thumbs-up and wave, I'm inclined to think a slight spinal compression; it would result in short-term paralysis (by which I mean six hours or less) and a general feeling of weakness or "jelly arm" in the extremities.
The lesson for the kids out there is this. DO NOT LEAD WITH YOUR HEAD!