Fun Fact! The yawn of a dog is not the same as the yawn of a person.
When your dog lets out a big yawn, you probably just believe it signifies the same thing humans do when we yawn: he's tired. And while it might be a symptom of exhaustion, dogs yawn for a variety of reasons. Dogs can yawn to settle themselves down, thus frequent yawns could indicate that your pet is worried or agitated. It's similar to how a cat's purr may signify a variety of things, so examining the situation's context can typically help you figure out what's going on.