Cerebral hypoxia can be caused by being at too high an altitude . But is extremely hard for a person to tell when it is happening to them because the onset of symptoms is subtle . It can cause someone to black out , stop breathing temporarily or die . Anyone on the plane could see a pilot take over , NORAD says .
Cerebral hypoxia can be caused by being at too high an altitude . It can cause someone to black out , stop breathing temporarily or die . Anyone on the plane could see a pilot take over , NORAD says .