To add just one more bit to this thread, I suffered an unscheduled loss of
cabin pressure in a Morane-Saulnier Paris II many years ago when I was young
and strong.  At 24,000 feet over Canada at the time I immediately exhaled
involuntarily and was amazed as my sight quickly went to tunnel vision with
little color.  I sat there some what stupified for many seconds before
reacting to the problem at hand.  It was really a shock to learn how fast
ones faculties depart and stupor sets in.  We pulled ourselves together and
started a decent while communicating with ATC.  We never did use the oxygen
as we got down pretty fast to a reasonable altitude.
I might suggest to those who fly high, wear the mask around your neck so you
only need to open the bottle to start flow.  You might want to take a safety
pilot along and do some research into your own personal critical altitude.
Walter Dodson   IV-P for sale (so sad)