There's Oxygen in our blood. It takes time for blood to oxidize (which we do through breathing and the distribution of O2 through our body), and if we rid all the oxygen from everything, we end up with unoxidized blood in our bodies. We would either die from an improper PH balance in our body, or from disease. Slow and painful. Everything dies.
You lose it all, and then it takes a very long time (I don't know exact numbers) to regain that oxygen. You could go days without the necessary amount of oxygen in your blood
if you hold your breath there is still oxygen in the blood. Also they are very calm and do not require as much oxygen.
Are we assuming that after the 5 seconds all the oxygen molecules are replaced where they were originally? If that is the case, the blood wouldn't need to re-oxidise as the oxygen it lost is immediately replaced.
Well in terms of breathing....5 seconds isn't long at all. And for the atmosphere, well... We'd be dead before the 5th second