Why does my dog look sad sometimes ?

My German Shepherd/Husky mix is 1year old. We rescued him a week ago from the animal shelter. At first he was very energetic! I didn't see him sleep the first two days :/. Now he still gets energetic when we play fetch a lot and take him out on walks 3 times a day which he loves ! !!!!! He's such a sweet dog, but when he's not in a energy burst he looks so sad. Does this seem normal for a dog getting used to his enviorment?

My dog looks sad often but its just her expression, not really how she is actually feeling. Since you walk him and exercise him maybe he is just really tired thats why he almost looks sad but really its because you wore him out! Which is a good thing. A tired dog is a good dog. (:Also, thanks for adopting from a shelter and saving a life!(:

Give him time...........my mom adopted a dog from a shelter that was abused beforehand........it leaves its effects. Anyway, he's young. Maybe he's just tired and resting.Its going to take more than a week for him to get used to a new, happy life. Remember, he came from a shelter. I'm sure he'll be thrilled he got a loving home.

He's probably hot or tired my dog does that on really hot days or after I have just played with him. It could also just be him getting used to his environment!