How are yawns associated with sleepiness?

Question

if yawns are caused by deprivation of oxygen, how does it have anything to do with sleepiness

Answer 1

It's just my own guess, but I think yawning has more to do with taking in more oxygen in an effort to stay awake.

Answer 2

If the brain becomes oxygen deprived, levels of consciousness decrease, producing a drowsy feeling. It's the subjective feeling of sleepiness that originally made people association yawning with sleepiness. It is, in fact, nothing to do with a need to sleep.