Posted for "Tom Hall" <tomhall@starband.net>:

Unless you are a serious smoker or otherwise quite impaired in your
pulmonary function, you will have no problems remaining consious and
performing once you get below 20k. Give it a try sometime. You will find
that while you may notice some vision acuity decrease and your mental
functioning may be slightly less acute, you certainly can survive.
(especially if your adrenaline is pumping after a engine failure!!)