MY dog is breathing fast at rest, then breaths normal. Is this a problem?

He was adopted last night. He does not seem to be in distress. He eats, sleeps, drinks normal. We notice it when he is at rest. He is still a little nervous. (he was at the shelter for about 4 months). He seems relaxed but is breathing fast. He is Australian kelpie/Lab mix. He is about 5 yrs old. Snuggling/petting him seems to help. He is asleep now breathing VERY normal and dreaming. Please offer suggestions.

he is just nervous about being in a new place, just pay him alot of attention and make him feel safe

He may have had some sort of trauma long before he met you. My dad accidently ran over our corgie (amazing he lived, my dad drives a dodge dule) and he didnt break one bone or anything, he was just super sore. Anyways, after that he would and still does the same thing. He will be breathing just fine, and then usually when he lays down he stars beathing really fast. We havent noticed a negative effect bc when he does it we stand him up and try to get him to drink some water. My mom noticed he does it more the hotter it gets (do you live in a hot or cold area?) So maybe your new dog has had something happen, who knows what and that is what causes it. But i know my mom did ask the vet (who x-rayed him etc after he got hit) And he said it was normal enough and not to be concerned.But if it does concern you then put your mind at ease and take him to the vet. Or you could call the shelter and ask them if they noticed it or maybe recocnize the symptoms and see what they say.Hope this helps!Good luck!