Tired Dog so Tired and Dozing

Why is my dog so tired?

The most common causes of lethargy in dogs are Infection, including parvovirus, distemper, kennel cough, and leptospirosis. Metabolic diseases, such as heart problems, liver problems, diabetes, and hypoglycemia. Medications, such as newly prescribed drugs or a new flea or worm product.

How do I know if my dog is too tired?

Watch for these common signs of fatigue:
He cannot perform the skill as well as he did earlier.
His interest in the treats or the way he takes treats changes.
He vocalizes frustration at you despite being quiet earlier in the session.
He acts too busy to do what you are asking him to do.
His form deteriorates.