Scubadiving and freediving (what he's doing) are essentialy the same, you are going to a depth thats quite deep then coming up again, as long as you come up without going thorugh a safety stop (wait for 3minutes at 5 metre depth) u risk getting the bends, it depends on how deep you stay, and the time you stay there. Its probably not slowed down because you actually fall like that in water....