Knock his breath out of him

what does "knock his breath out of him" mean? Is it apprehension or awe or surprise or something else?

If someone or something knocks the breath out of you, it's because you got hit hard in the chest, or were thrown around physically in such a manner that you had to catch your breath afterwards. Something to which you react with awe and surprise, on the other hand, takes your breath away.
SS