I agree that a visit to the vet is warranted. Chewing the paws can be a sign of allergies, and if severe enough can cause listlessness as well. He could have been exposed to something in the kennel that promoted an infection - since dogs have sweat glands between their toes - staph infections are fairly common on the feet (hot spots). They could've used some kind of chemical to clean the kennel that he has had a reaction to. I would also look for a medical reason before I assumed that it was depression related.
I hope he feels better soon!
