[papabrown]

I’ll also add to my previous comment and say that the reason you’re taught slow, diaphragmatic breathing is because your lungs impact your buoyancy in the water.

Breath in, you begin to ascend. Breath out, you will sink.

Your goal is to find a breathing pattern that allows you to stay neutrally buoyant so you’re not fighting the rise and fall by swimming against it.

Part of the instructor exam, at least when I took it, was a pool session where they tested your ability to achieve and maintain neutral buoyancy.

You would sit cross legged holding your fins for balance like a meditator half way between the bottom and the surface and you could not rise or fall more than a foot.

It’s something a lot of divers also practice when doing safety stops. Even if there’s an ascent line, many will simply stop at 15 feet, and watch their dive computer trying to maintain exactly at 15 feet using only their breathing.

The reason for that is often there will be no ascent line or you may have to do decompression stops in open water with no physical point of reference.