Here's how you might survive without a ventilator, from NYT :
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Instead of quickly sedating people who had shockingly low levels of oxygen and then putting them on mechanical ventilators, many doctors are now keeping patients conscious, having them roll over in bed, recline in chairs and continue to breathe on their own — with additional oxygen — for as long as possible.
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But here you will need a oxygen tank anyway, Which might not be available.
It also talks about people that are dangerously low on oxygen, still being able to talk over phone as if they are upright, which wasn't seen in any previous disease. Of course they will suddenly collapse, if not assisted right now.