This common physiological behavior has been the subject of decades of research hoping to unravel the mystery of this simple expression. Aside from many cultural beliefs applied to yawning the scientific communities are attempting to debunk many earlier theories and get to the bottom of this mouth gaping response.
For years it was considered that we yawn simply because we are bored, tired or our brains need oxygen. What happens when we yawn?
Here's the basic idea:
- When you start to yawn, powerful stretching of the jaw increases blood flow in the neck, face, and head.
- The deep intake of breath during a yawn forces downward flow of spinal fluid and blood from the brain.
- Cool air breathed into the mouth cools these fluids.
Why is it that we may yawn at visual or audio stimulation of others yawning? Recent research affords new insights about the social empathy of humans when responding to the yawn stimulus. Is it time we change our ideas about yawning? 
In conclusion, go ahead and yawn – the benefits are many…and if you are drifting off during a long-winded meeting plagued with repetitive sensations to yawn, do it! You may want to cover your mouth to be more discrete, however, do let yourself experience the fullness of the experience: jaws open wide, breath flowing in, desire to stretch your limbs. Enjoy the momentary relaxation that accompanies these movements. Your body will thank you for it.
And if others join you in mirroring the act, delight in discovering perhaps the more socially developed empathic individuals around you. 
Author: Nancy Newman, LMT