Given respiratory/oxygen physiology is my bread and butter (I'm an anaesthetist/intensive care doctor) and rely on ventilators and supplementary oxygen, the oxygen you require is completely dependent on a) how much you are using - being anxious/engaging skeletal muscle for fight or flight/increased heart rate etc and even pain can increase oxygen requirements many times over - you need a flow rate that provides 250ml a minute at rest for average 70kg male. It can be more than this of course that is required.
it might be difficult to obtain this purely via a nose - many of us naturally have deviated septums etc - then a struggling person would go limp, their muscles slacken, and oxygen consumption reduce, meaning it became an adequate flow rate again.
the other issue at hand is actually CO2 retention. If carbon dioxide cannot adequately be breathed out and exhaled it will accumulate and make you drowsy. Very drowsy. Almost dead looking
this would be the issue with small spaces/insufficient fresh air and masked faces if the material is not porous (duct tape is not, filter masks are!). This i personally find a more physiologically valid reason for transient loss of consciousness.
the third medical reason is a state of traumatic fugue. It genuinely is a thing for trauma to eradicate the way the part of the brain responsible for transferring working/real time memory into storage. In high stress/cortisol/adrenaline the hippocampus which usually gives us a what/when/where context to emotional recall of an event just stalls leaving only emotion and no explicit ability to recall anything but fear and how we felt. That's the amygdala. I once met a man who saw his wife get murdered in Iraq, and he has forgotten who he and the rest of his family were. Even his twin brother. Twenty years later still no idea. Not faking it, his brain simply didn't even light up in the right areas of the functional MRI scannner when shown familiar faces/photos of his old life, unlike nurses he knew in the present.
i am growing increasingly suspicious again of the husband as you all say. The therapist wouldn't be relevant to random break in, unless she knew a third party knew about the money. I think they were having issues. Post natal depression can be incredibly serious and psychotherapy is the most evidence based intervention for mental health - GPs can only medicate not give psychotherapy, and the medications don't have the same wealth of success.
So yes, the transient hypoxia thing doesn't make a huge amount of sense, but also could be true physiologically (I've seen patients go hypoxic and drowsy just from shivering - you can measure oxygen consumption if they're on a ventilator, and it really does go up in high arousal states!)
