Looks like the rumours last year that the French were complaining about the content of HPL have come true.
This goes back to diving physiology don't remember doing it in HPL
The breathing into a bag is because the rate you breath is related to the PH in your blood which if you are hyperventerlating is extremely low (low CO2). This puts your body into shock which increases the panic level. Breathing into the bag increases the CO2 to normal levels which allows the body to come out of shock. Then lets the brain to recover control.
In diving this can be a very bad thing because if you hyperventilate then hold your breath the body gets its trigger to breath from the PH level (carboxy acid I think). So you can run out of oxygen for respiraion before the body gets its trigger to breath. So you just pass out. Which because we need a consuious thought to keep the demand valve in our mouths, usually leads to death unless you buddy spots it in time.
MJ