It's too cool for you to worry about heat stroke but I would still be concerned.
I would be most worried that you are seeing symptoms of heart disease and would suggest that you see your vet tomorrow for an EKG and possibly an ultrasound if the exam proves this theory.
When the body is at rest, it taxes the heart every time that you wake up, partially because of the movements of the body and partially because of the extra respirations required. So, this could be why you are seeing these symptoms.
You might also see a cough, noise, or increased respirations when eating and when the dog is excited.
So, go ahead and see your vet again tomorrow and have him rule this out.
Aside from that, stress and pain can cause what you are seeing. So, do take this seriously.
Let me know if you still have questions.