Having a bad day?

Have you ever wondered how animals have a bad day? Yesterday seemed to be a bad day for a lot of the humans I came in contact with which meant my day was far from perfect but it made me think about what happens when animals, especially the shelter dogs I deal with have a bad day.
How would you know? Are they more scared or less? More jumpy and spaced out?
I think given the situation they are in, they must have more bad days than good. Can you imagine not knowing where your next meal is coming from? We know they will be fed every day, but they don't know that.
Or that the dog in the next kennel may threaten them to the point they hide in the back of the run. They don't know the dog cannot get to them. We do, but they don't.
Imagine losing everything you knew. Every smell, person, situation, and being placed in an environment where everything was different from what you had known your whole life.
Then, just when you think everything is going to be okay, all these strange people pass by your kennel and stare at you and talk about you. You have never seen these folks before and don't know what to expect. You don't know they are looking for a new pet, or if they are nice, or really anything about them.
Although I am convinced shelters provide many more good days than bad for these dogs, you have to wonder how to tell the difference.