Maybe it’ll happen on the long trip to Kota Kinabalu, when you realize you’ve lost two days to time zones. Or maybe it’ll happen as you squirm into your life jacket while crossing the Mabul Passage.

Imagine flipping over backwards off of a boat and into crystal clear waters down below. You're all geared up with your BCD, regulator, oxygen tank, wetsuit and fins. Together with your divemaster, you ...