From watching the video, I'm guessing he ran out of breath. Hes in snorkel gear not scuba gear. He was down there quite awhile. Most people can't hold their breath longer than a minute. Maybe two minutes if your in good shape. Underwater even less because of pressure and the energy that you're expending swimming. Plus not sure how long he was down their before the video started. Ironic. He literally couldn't hold his breath long enough, just like he wrote in the proposal.
