Well to be fair, he didn't have access to his healing skills and what was sleep when insanity was clawing at your subconscious. He may not be out cold for long, but considering some old injuries, it shouldn't come as much of a surprise that one punch finished him off.

Surprising since it wasn't noticeable before, huh.

He will be OK, Nanako. He only really is in need of a nap (and to be dragged down to a floor that does not enable powers to be used). Seriously.