I developed the same thing two years ago... One of many sporadic, but progressively worsening side effects. Mine was from an adverse reaction to the H1N1 vaccine (but I'm learning any vaccine, virus, or toxin can trigger dysautonomia). What I experience feels like I am going to yawn, but instead, I end up doing several (2 to 5) quick inhales, then it just all stops. It never develops into a complete, stretching-type, fulfilling yawn.
During one of my episodes, (an episode being lightheadedness, fatigue, brain fog (like brain working on half-impulse power), memory issues, out of breath with the littlest effort (walking down the hall can do it when I'm really bad), etc.), I will start having these "incessant yawning" spells.
Pulmonary function tests all looked normal except my diffusion rate, but 1-1/2 years later they found out I no longer properly metabolize oxygen so it isn't my diffusion rate, I don't use the oxygen in my blood, so the blood-oxygen level is highly saturated when the blood returns to the lungs so it shows as a low diffusion rate, it's really low VO2. Putting together what all my ten-and-counting doctors have told me, my "guess" is, when I metabolize less oxygen, even though I am inhaling and maintaining plenty of oxygen in my blood, the muscles/organs aren't getting it through a failure to metabolize. That triggers the signal to the brain (from any body part struggling from lack of oxygen) that I don't have enough oxygen, triggering the response to "gasp" for air.
There are several points this process can go wrong and thus trigger such a yawning response... breathing in the oxygen (asthma issues), diffusing oxygen from the lungs to the blood (pulmonary diffusion), delivery to the body part, anywhere in the process of properly metabolizing the oxygen as energy source at the cellular level, and I'm sure there is more but you get the picture. So it isn't a simply answer to the question of why? Hope that helps.
I do have 2 questions, can she be anemic. i am and man oh man I get tired. I yawn all of the time, even though I seem to sleep fine and trying to go upstairs I get winded, they say it is due to being anemic (not all anemias are related to the way you eat) My is due to heavy periods.
the second one is could she have sleep apnea? how did they rule out asthma. have they done a PFT(pulmonary function test)
My friends son is also going through this with football, he would actually pass out and they told him the same thing. (hyperventilation) then they had him doing a stress test and he did the same thing and now they are waiting the results of his test.
Good luck and I hope you can get answers
michelle