WARNING
You should not try this at home alone or unsupervised. The experience I give here was under the watchful eye of trained professionals. Please do not attempt this.
How long can you hold your breath for?
When I was a teenager I used to practise standing and then walking on the bottom of a pool. This was done by letting all the air out of your system and making your body 'dead weight'. It was a real art. It first started when I was doing a merit badge for swimming/life saving in scouts. I kept doing it until I could walk alost the length of the pool - but it was really difficult.
However, while holding oxygen I think my best was 83 seconds. How about you? Do you have any phobias about holding your breath or being in water?