I have also read all of the things about hypoxia in the AIM, and I think they are a bit exagerrated. I am in good physical condition and don't smoke, so I should last a little longer and get more oxygen than someone not like me, but I have never experienced shortness of breath, headaches, lightheadedness, loss of color in vision, blurred vision, or anything else while flying above 10,000' in a light airplane. I have gone up to 13,000' in both night and day. I 5 hour night flight at 11,000' would be a different story, of course, especially for someone who lives at sea level. Maybe that would warrant bringing and using oxygen, or cruising at a lower altitude.