Some dogs breathe faster and heavier than other dogs. This is known as brachycephalic breathing syndrome. The group of brachycephalic dogs includes dogs such as Pugs, French Bulldogs and English Bulldogs.
While this sleeping stage lasts, your puppy might be restless and may even move parts of its body or mumble. Also, there is a large possibility that your dog will breathe rapidly during this phase of sleep.
If your dog seems to have difficulty breathing, with no apparent reason you can see, it is possible that the dog is in pain. You may not have been paying attention, but there might be some other symptoms present in your dog.
Perhaps, for this reason, you have acquired various games that your dog can use to make the time pass faster while you are away. Maybe you have been exercising your dog more intensively in recent days.