Pia is dead on. Any pilot who plans to get above, say, 5,000 feet MSL or so ought to understand his/her response to hypoxia. Although there are common symptoms, each individual needs to learn just how it will feel and how to recognize it.
The best way to learn is in a controlled environment such as an altitude chamber or in a hypoxia simulator. The best place to learn is at the Civil Aerospace Medical Institute at FAA HQ in Oklahoma City, OK. They have an amazing array of equipment and courses available, including an altitude chamber, an hypoxia chamber, spatial disorientation devices, simulators, survival training, ditching training, and lots more. The best thing is, it's all free! All you have to do is sign up and get there! You must be at least 18 years of age and interested in aviation. You don't have to be a certificated pilot.
Formerly, civilian certificated pilots were able to take this training in military altitude chambers, but that option has been taken away. For now, the best value in aviation training today is found in Oklahoma City.
They book 90 days in advance and the available slots for training fill up fast!
I have to take exception to the idea of flying with anybody to altitude in order to experience hypoxia first hand. There is just too much that can go wrong in such an uncontrolled environment. It's pretty difficult to simultaneously fly an airplane and to try to deal with an incapacitated passenger. Leave such training to the pros!
Harlan Ribnik, MD