decompression sickness. Being that nearly all snorklers don’t drop below 33 feet and not using a tank, there is very little risk to snorkeling and air travel being so close together. The main problem would be fatigue after flying and then identifying drowning. Snorklers are face down and won’t give off signs of drowning. Thus any accident inhalation of water isn’t easy identified. Combine that with fatigue, drowning is easier and quicker.
Bottom line: Don’t swim in the ocean if you’re tired and go with a buddy.