Small dog could be sick? HELP

ok so I have a small min-pin mix and all of a sudden he is shivering, constantly licking his lips, wont go outside and go potty, wont eat, and acts like he is afraid of something but there is nothing around to hurt him. he is fine under a blanket but he doesn't look very comfortable when he moves/walks and will only fallow me, yesterday we had to "put down my rat" (we just shot the poor thing to put her out of her misery), could her death and absence be affecting like him like if a human mourning (I was crying a lot). this all started today.

Personally, I would be somewhat worried about rat poison. Is there any of that around the dog could have gotten into? At the neighbors? I mean it might just be reacting to you emotions but that licking lips thing... rat poison is nasty stuff.

Sudden behavioral change like that is definitely a clue-in that something is wrong, likely illness or injury. I'd honestly try and get in with the vet ASAP- not necessarily an emergency vet, but like, tomorrow- and get things checked out. Lip licking and shivering can be signs that a dog is in pain, even if they don't have any specific tender areas that you can find hands-on. (My personal dog experience says "eek, back injuries!"- but well, my first dogs were corgis )

Was your dog ok before you put your pet rat down?
Were they friends? Sometimes animals will get attached to one another. Just guessing here. I saw a show about unusual pets being friends. When they were seperated, they went into mourning. One case was a goat and a donkey. The goat would not even get up to eat. And just lay there. Till they figured it out and got the donkey there.
Did it hear the gunshot? Some animals fall apart hearing one.
If neither is the answer, I would most definately take it to the vet.
I think I would anyway, just to be safe.
I hope your dog is ok. Let us know ok?

When a dog won't eat for more than a day, I think a vet trip is in order. Hope things work out alright.