Can you both sleep and yawn at the same time? If not, why don't we?

Answer 1

Usually we don't do both but could possibly happen. A simple explanation is that yawning is due to low oxygen levels in the blood stream which causes you to take a deep breath when you need some extra oxygen. Yawning can grasp an amount of air that could give some relief to the need of more oxygen.

During sleeping, the body relaxes and not doing "hard work" thus needs less oxygen and so yawning is most commonly not to occur as there is no need for extra oxygen.

However, sleeping does not always guarantee having adequate oxygen supply. There are circumstances that some "unknown mechanisms" occur while sleeping. So, it won't be a surprise to see someone yawning while sleeping though such situation occur very rarely.Afterall yawning is a semi-automatic reflex that originates in the brain stem in response to a lower level of oxygen in the brain.So to say, such reflex can possibly occur while sleeping.

Yawning can also occur when someone gets bored, when someone gets hungry or sees someone yawning.

There are still lots of unexplainable things about yawning so we cannot give a definite explanation for now.....