... I did wonder how painful a fast ascent from the bottom of the ocean would be once the bends kicked in, but had enough sense not to raise this question with about a quarter of the crew in earshot.
For an approximate simulation, imagine what removing 90% of the air from your lungs might feel like.
I don't have to imagine what removing air from my lungs feels like: that is part of breathing! Anyway, this guy seems to do OK compressing his lungs even more:
http://competition.the-french-job.com/spread-the-world-recor...
Physiological freaks aside, go too deep, and you're dead. Especially when you go from 1 bar to, say, 15 instantly, which is a situation that free divers do not expose themselves to.
You know that pain you get in your sinuses and ears and other air-pockets in your body when you swim to the bottom of the deep-end of the pool? That's from a pressure difference of like .3 bar. Now imagine something 10 times that.