I have pitbull, american bulldog mix, shes 14 months old. Her jaw shakes or locks when shes tired an yawns or is just waking up. Its happening more often lately. Its like a tremble almost (hard to describe in writing). There is no drooling or other weird behavior, she eats fine, has plenty of energy etc. Just wondering if this needs to be checked out by a vet, I am getting more concerned. Ive tried to research it online but havent found any situations that seem to match hers.