[renox]

I don't know if this related to this effect or not but I've noticed that it's much much easier holding your breath for a longer period of time when you're in a swimming pool than outside.

[tarsinge]

Be careful to not push yourself and to never do breathing exercises with retention in water, the risk of fainting and drowning is real.

[renox]

True, and we did it in 'pair': one is watching the other doing the static apnea, and then we swap roles.