A couple goes out to the Gulf of Mexico and they get caught in the current, pulling them away from their anchored boat... leaving them stranded for more than 24 hours.
Wow! They are so lucky to have survived, considering that no one even knew they were gone!
SCUBA diving is a very zen activity. I haven't done very many dives yet (can still count the total on my hands) but I've noticed that staying calm is key to good diving. It is all about breath control and peace to conserve your energy and thus, your air.
Unfortunately, the fact that you try to have this sense of tranquility under water does not make it a safe activity. Just like hiking (or almost any outdoor activity,) you should always tell someone where you are going and how long you will be out there, just in case something bad happens.