By some strange twist of first quarter plebe year fate, I won a swim-off the first day of class and got promoted to the open spot in the advanced group. The rest were all on the swim team. (I blame knowing how to do flip turns, I'm not that fast a swimmer). Holding formation while treading water in the deep end, dressing right and reporting and all. Crazy class. We blazed through survival swimming in 10 lessons and then did the pool portion of SCUBA.
The thing that scared me the most was being told to exhale all the air out of my lungs and let my body just sink down until I was lying on the bottom of the pool. In the deep end. Hard not to panic. Huge confidence booster once I'd done it, and a real lesson in how your body moves in water with air in your lungs, and no air in your lungs.
Funny, my breath control has been really good since then, and I don't panic in cold water or open water swimming any more. DPE: so easy to hate, but so good for you.