Should I be worrying dog sleeping under the covers?

I used to worry about dogs sleeping under the covers but they do seem to be fine. My current dogs sleep in their crates but when I was a child, our family dog slept under my covers or under the covers of my brothers. It depended whose turn it was for our dog but he always slept under our covers. Every morning, he was bright and alert, so if he didn't get enough oxygen all night long, he was still perky and bright anyways.

Perhaps check with your vet. Many dogs sleep under the covers and I don't think it is a health issue but if you wonder, check with your vet.