What is known/taught about yawning during meditation?

At some point in life I learned I could focus on some bodily awareness that resulted in the following experience: - Piloerectus; Not once, but it stays throughout the meditation while I keep on focusing. - A smile is slowly coming on my face (slowly as in it could take 20 seconds or so). It intensifies when I focus on that particular bodily feeling. It feels mechanically. When I take a picture of this I genuinely look happy. - Yawning; I cannot suppress this yawning when I focus on that particular bodily feeling. I yawn almost every minute intensely. - Energy swirls through my body. which can even make pains go away. Like pains from stress as facial muscle cramps or so. This all can instantly go away when I have thoughts of doubt, fear, resentment or any other negative thought. The smile and energy swirls I understand. Why piloerectus and yawning occur I do not. I am not feeling tired at all when the yawning happens. And when I stop to focus on this particular bodily feeling, the yawning stops. I do not yawn during a whole day, for instance. To me the yawning is a reproducible sign that indicates whether I am focused or not during meditation. But why does it happen? In this pubmed article it is described that yawning is controlled by dopamine release (amongst other neurotransmitters). I was wondering if there is something written about this yawning during meditation in the teachings of the Buddha.