Aloha! You're speaking to Dr. Michael Salkin
I'm sorry that your question wasn't answered in a timely manner. Such breathing has quite a few possible etiologies. How old is your dog? Which breed is your dog? Is your dog neutered? Does your dog have pre-existing medical problems? Is your dog currently being administered medication?
Your dog's breathing can represent both medical and behavioral problems. It's often seen with elevated ambient temperature, exercise, anxiety, or perceived pain. To confound the diagnosis further, it's also seen with fever, narcotic administration, glucocorticosteroid (prednisone, e.g.) therapy, Cushing's disease, hyperthyroidism, hypocalcemia, pheocromocytoma (an adrenal gland tumor), cardiac disease, tachyarrhythmias (fast irregular heart rates), brain
disease and obesity.
I regret that I can't be more specific for you from here. If such behavior
persisted for more than 36 hours, it would be prudent to have your dog's vet perform a thorough physical exam perhaps including blood and urine tests as well as thoracic X-rays to better assess his heart and lungs.