It doesn’t look efficient to me!!!As a matter of fact, it looks fairly restrictive as you’ll need to be able ti breathe in a certain way which doesn’t appear “normal” by any stretch of the imagination.
I’m not afraid of monsters; however, I find it necessary to cover my head during the coldest nights of the winter months. I’ll pull the covers over my head to help me to warmup when first laying down. Then when I get to the place it’s uncomfortable to breathe, I lift the covers about where my mouth is & flip it back so I have a natural breathing space at my mouth with the rest of my body covered by a cozy blanket!!! For those scared of monsters, your eyes are still covered so you can’t see them & they can’t see you yet you can still breathe fresh air!!! Try it to see IF it might work for you!!!