Holding your breath

[keef]

word of warning here......................
if you hyperventilate (take several deep breaths) before underwater swimming as several people here have mentioned, then the drowning reflex, which is the burning desire to surface and breath, can be subdued due to excess co2 in the lungs, which means you don't try to surface until it's too late and you drown.

It has a name, which I'm sorry I can't remember, but it's one of the first things they warn you about on a freediving course. Most freedivers only take two deep breaths before diving for this reason.

Please be careful.