It might be easy to assume that dogs have an easy life. It’s eat, walk, play, sleep, repeat. What could possibly be stressful about that?
Before you assume you know exactly how your dog feels at all times, keep in mind the basic needs of dogs:
sufficient rest and sleep
sufficient mental and physical exercise
access to water
sufficient opportunities for toileting
good physical and emotional health
comfortable social structure
ability to make choices
The lack of one of more of these could, and likely will, result in stress for dogs.
Notice also that “sufficient” could be different things to different dogs; frequency of rest, food, exercise, toileting, etc. depends on factors such as a dog’s age, energy levels, genetic makeup, and state of health. Young dogs will need to sleep and eat more often, older dogs may need to sleep and pee more and have shorter but slightly more frequent, slow walks.
How do you know what’s sufficient? By knowing and observing your dog. For example, some dogs are pickier eaters than others, some dogs more active than others, and some dogs more sociable than others, so comparing one dog to another would not help much in understanding what is normal or sufficient for individual dogs. You need to observe them and know their habits, routines and behaviours when they are well in order to know what is normal for them as well as to recognise when something is amiss.