There have been some recent airline crashes in the news lately, even some small single engine accidents have made the major news outlets. One of the most recent was most likely caused by Hypoxia.
Hypoxia comes in many different "flavors" from the innocent hypervetalation, to toxic hypoxia. Hypoxia is really the inability of your body to properly process oxagen to the body, and how this process is inhibited is the type of hypoxia you have. At some point your body -not able to get oxegen - will shut down and faint using less oxegen. If you do not get a steady supply of oxegen soon you will die and it happends all too often.
In pilot training they train you to recognize the symptoms of Hypoxia and how to effects your body unfortunity at some of the altitudes commerical aircarriers fly at if the aircraft looses pressurization and you need oxegen your supply is often not enough to get to a safe altitude. It takes a freek of nature to cause an aircraft to loss pressurization and fortunitly is very uncommon.
The general public should learn about Hypoxia and learn to recognize the symptoms as well, because it could save your life. All US carriers are required to have addiquite supply on board, but in some countrys of the world this is not the case and as has happened with the most recent of those crashs the pilots surcomed to Hypoxia and lost control of the aircraft, and consquently crashed.
A simular thing happened to Pain Stewart the famous gulfer in South Dakota a few years ago. He was in a private jet that some how lost pressurization and the crew did not respond quick enough and all souls on board where lost.