When they fall down in front of you on an airplane, it is generally not very reassuring. Following a sudden loss of cabin pressure, oxygen masks allow passengers of commercial aircraft (and its crew) to breathe normally until the aircraft reaches an altitude where they can breathe normally (about 3,000 metres / 9,800 feet).
In the event of depressurization, the passenger service units (PSU) for passengers, is not the only one on board aircraft; for example, a first aid system also ensures an oxygen supply to a passenger with a heart condition, for the duration of a flight. But that does not tell us what the autonomy of oxygen masks in aircraft is.
The answer is at the end of this video, but before that, listen to the passengers’ answers to whom we put the question in an airport.