Comment by aqme28

There are two gases that need to be exchanged when you breathe. You need to get rid of CO2 and you need to get O2. When you hyperventilate, you purge CO2, but don't really change your O2 content.

This matters only because CO2 is what triggers your desire to breathe, but O2 is what causes you to actually pass out or not. So what happens is that you might pass out before you realize you need to come up for air.