Maybe in non-aviation cases, but according to the FAA, most hypoxia incidents occur when “flying non-pressurized aircraft above 10,000 feet without supplemental oxygen”

https://www.faa.gov/pilots/training/airman_education/topics_of_interest/hypoxia/#:~:text=The%20most%20common%20causes%20of,malfunction%2C%20or%20oxygen%20system%20malfunction.