He's in pain, of course! Take him to the vet! NOW!
He could be having an allergic reaction to something.
You need medical intervention for your dog, not a wiki answer. You should take it to the vet as soon as possible.
The dog has an injury probably got while playing.
If your dog is female (a bitch) this sounds a bit like morning sickness. She could be pregnant.
That could be due to a number of things, take the dog to a vet to decide whats wrong.
whats the size of a dog
a dog in a costume whats so hard about that
You have a dog that is shaking, hiding in th dark and won't eat and you are asking on WIKI answers? Geesh, take the dog to the vet for Gods sake.....
whats a verb for dog?
No. A dog has to do what a dog has to do.
It is possible your dog has canine lupus or another auto-immune disease; these can show up as color changes or irritation of the nose.
Jack