Anytime you are thrown off balance as in being knocked down or falling it is an instinctive react

‘Anytime you are thrown off balance, as in being knocked down or falling, it is an instinctive reaction to “catch your balance”…When your breathing is physically restricted we start to panic and no other thought exists except to free the restriction and get the breath in. It is so overpowering that merely placing a hand over someone’s nose and mouth triggers the response…There is a huge portion of our frontal cortex that is dedicated to vision and when our vision is obstructed there is an overpowering urge to clear the obstruction. Just putting your hand over the opponent’s eyes will cause him to react.’

Emerson, Ernest. The Seven Strategies of Hand to Hand Combat: Surviving in the Arena of Life and Death. Createspace Independent Publishing Platform, 2015, pp. 30-34.