Hello, Joyce and welcome!
My name is ***** ***** I will be glad to assist you with your question about Bennett.
I'm sorry his symptoms have you worried.
I'm glad he's not showing any signs of difficulty breathing, outwardly, but when you can see his sides heaving in and out, as he breathes, this may indicate a respiratory or other problem. Some common causes of this symptom may include heart failure, asthma, pain, lymphoma, stress, just to name a few.
Even though he's eating and playing as usual, I would still advise a visit to the ER vet center, to have him evaluated in person. X-rays will help determine the underlying cause of this symptom. Sometimes, they will put him in an oxygen cage to help calm him down, so x-rays can be taken.
I hope you're able to get him to an ER vet, asap and please let me know how he's doing and what they tell you. Thanks!
I hope all will be well with your Bennett!