I used to dive into the deep end and then swim laps, I'd go way DOWN first though, as I loved to be deep underwater. Then one day when I was working out in the gym doing some yoga in a class I guess, some water came pouring out of my ear all over the place! I had not known it was in there. Now, my ear drains every day. When I lay it down on my pillow at night, it drains out, but I have not been swimming in years!
I had ear infections when I was a kid and then had one in my mid 30s that would not go away for 6 months. Drs could find nothing wrong with the ear, including a specialist, though I do have hearing loss.
I think it was the deep water swimming, the pressure under the water, day after day, that did it. But who knows... I don't go swimming any longer, though I did love it and also loved it when I was a kid.