system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how come if I try and sleep under the covers I get too hot and oxygen starved and have to come out after a short period of time, but my dog can sleep under the covers all night long?
gpt
Your dog's ancestors slept in a den or burrow, he is adapted to the stifling feeling and it may even bring him comfort. 

This is also why dogs eat their own poo... if they are hiding in their den or rearing young and can't leave, it keeps the den clean and prevents smells that attract predators.