Hypoxia affects everyone differently, which can make it difficult or even impossible to tell when you are being affected by it. Hypoxia can occur rapidly or gradually, and it is important to understand the risks.
The video linked below shows someone entering into a hypoxic state. You can see that he is gradually losing concentration and becomes unable to identify basic things.
Additionally, notice that the person does not seem to be nervous or worried about his worsening condition, as he is unable to notice his loss of brain function.
Video - HypoxiaThe true danger of hypoxia is that a person can often times not notice their own worsening condition. With almost any other risk or condition, proper attention can generally minimize the level of danger. However, hypoxia can creep in without the victim even noticing.
Once the person is in an impaired state, they can become unable to help themselves or make safe decisions.
While the symptoms can vary widely between individuals, the following symptoms are common:
In part 91 operations, supplemental oxygen is required under the following conditions:
Remember that the above requirements are only the legal minimum. It is recommended to use supplemental oxygen at pressure altitudes above 10,000 feet MSL during the daytime and 5,000 feet MSL during nighttime.
The linked FAA brochure below outlines some additional information regarding hypoxia:
FAA Hypoxia Brochure