If your oxygen drops, breathe lying on your stomach with a fan in front of your face. This takes your SpO2 up by 5-6 points.

The doctor who treated me while I was hospitalised, has advised this to a friend of a friend. Let's hope you're able to find oxygen when the need arises, and don't have to use this technique. Also, happy to connect you with my doc in case you're feeling unwell.