I'm not sure. I read in a medical book that dogs can get some type of depression, for whatever reason, but it is difficult to diagnose.
Mine definitely sulk. I know a lot of people (non-doggy people, mostly) say "its a dog...it can't sulk" but honestly I think they can. Mine, for example, are miserable when made to go out in the rain. Maisy hates the rain the most and walks behind us, head down, sloowwlly when normally she would be running about with the others. If THAT isn't sulking I don't know what is!
It doesnt sound that much different than what humans might experience. And that isn't surprising...I know lots of folks with dogs and cats and both species have what I would consider days where they are blue. They all perk up tho with some attention and exercise.
I believe it.. my folks have been gone for 2 weeks (coming back in a week) and Saba mopes around, sleeps a lot or just lies down and looks sad most of the time - unless I play with him or take him for a walk. My mom doesn't work so she always takes him for walks about 2 times a day when I'm at work. He goes to their bedroom and leaves toys on their bed.. probably thinking "hey, got you a present - will you come back?" lol.. or just lies on their bed which he never did before.
so yeah, I think they can feel depressed from time to time. it will probably pass.
When Emilu was gone for 9 days at the stud dogs kennel, Skippy only ate twice the whole time. As soon as she walked back in the house, he ran over to his food bowl and started eating. He doens't even act like he even likes her half the time, but he sure depends on her.