This is also a gesture in stressful situations for your dog. It does not necessarily mean that it is sleepy. Dogs also yawn when they are anticipating something good. Many dog owners have found that their dogs yawn when they are happy. So yawning could be a good thing too, depending on the situation.
10. Tail Tucked In
This is generally an act of fear. Dogs tuck their tails in between their legs when they feel threatened and scared. Remove whatever is scaring your dog or take your dog away from there. However, this could also mean that.