The recent depressurization of another airliner got me to thinking and remembering a "high altitude" incident I experienced many years ago.
When I was a young buck flying a C-172 between Syracuse and Boston vfr I ended up at 15500 feet to get over a large cloud deck. Now that's pretty high without supplemental O2. I did ok but did feel a bit light headed. Luckily it was daytime and the clouds were nice enough to dissipate over central Mass. Supplemental oxygen would have been helpful and should have been aboard. Part 91 of the FARs states that you can only fly between 12500 and 14000 feet for 30 minutes without supplemental oxygen. Above 14000 ft the flight crew must have O2 and above 15000 ft all passengers must have supplemental O2. This of course is in a non-pressurized aircraft. The high altitude rules for 35000 ft and above are interesting. Look them up. Just google FARs.
Well, keep safe and use your O2 when needed to keep from getting anoxic.