Nobody can take a hit like that and be fine afterwards; Barrow, who didn't see it coming at all, makes a sound like a wounded bronto as the chair takes him down. This might be enough to incapacitate a smaller, less lyrium-starved person, but in Barrow's case-- as with any other big game-- it really just serves to piss him off.
He's on the floor when he turns to launch himself into Lazar's legs in a full-bodied tackle.