Well, I had an advantage in that I practiced becoming a Weekie Watchee Mermaid from about the age of 4. Part of that required being able to hold your breath for 30 minutes at a time. Dad took us to see them when we lived in Florida. It wasn’t until I was much older and saw a video that I realized they had access to air hoses and they weren’t hold their breath for 30 minutes at a time!
As a kid, though, I could swim the length of an Olympic sized pool on one breath. I was was totally at home in the water. I’d release my breath until I was standing on the floor of the deep end, then I’d to gymnastics, back flips and stuff.
The only time I got worried was at a lake. I dove off the high board determined to make it to the bottom of the lake, having NO CLUE how far down it was. I made it, but it was a little freaking getting back up, running out of air with no idea how far from the top I was. Scary.