Welcome! My name isXXXXX am a UC Davis graduate, and currently, a Medical Director of a veterinary hospital.
I am sorry to hear about this concern for Bryn.
Well, at this age, and for increased lethargy, I would have to be suspicious of a few things:
1. Progressing arthritis may be causing Bryn discomfort
2. Hypothyroid. Low thyroid hormone, which is very common in older dogs, can cause complications
3. Other systemic (internal) illness.
So, it definitely sounds like it is time to get into a vet for a routine examination. In addition, some basic testing would be well worthwhile!
A canine basic blood test and a urine test (urinalysis) may answer a lot of concerns, or at least rule-out many possible explanations.
What can tests tell you:Chemistry Panel CBC (complete blood count)Urinalysis
- ensure a thyroid level is included on the blood test to rule-out hypothyroidism (low thyroid hormone) and quite common in middle to older aged dogs.
Very sorry that it appears he is so lethargic, but it may be correctable to some degree if a specific cause is identified and medically managed.
I hope that information has been helpful.
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