First two rules of scuba diving:
0. When you enter the water, you enter the food chain.
1. Keep breathing! So your lungs don’t implode / explode when you hold your breath but change your depth, altering the water pressure on your body.
I went on a snorkle boat on the Great Barrier reef. We snorkled the shallow reef, and then went out deeper. At the deeper area they said scuba was available, and they would give “lessons”.
The “lesson” was - “This is the breathing thingy. Put it in your mouth and breathe.” I was old enough to know better I suppose, but paid my money, strapped on the gear and jumped in. No buddy, but I figured enough other people were in the water. Except by the time I was in it seemed like I was all alone.
Really cool though! A huge shark swam below me - I tried to go down a bit closer and keep up but it was way too fast. Saw several of those HUGE clam shells - like in the Popeye commercials. Looking back it was really stupid - still have sinus issues 30 years later. But it was amazing.
Was about the only thing I’ve ever done that lived up to my expectations from what one sees on T.V.