I have been here for about 3 years (lurking for a couple of years and 1 year online).
And I am so mad at myself because I was here at a time when it was so much easier to get N, but did not.
I have read that people, even when unconscious may pull the mask off. Not sure if these threads are still around.
I think if the set up is done perfectly (diving mask -costly, making sure one has pure inert gas, and the hands cannot interfere), it might be ideal; however, it is too complicated, and right now too expensive for me.
Also, it may be that they are not entirely unconscious when this happens/still getting some O2
I am not sure, but am not willing to risk it (my opinion only)
<3