I think you should call your Vet as soon as possible. He/she may want to see him or can can give you some advice over the phone. Be safe! Call the Vet !
My dog just had another dog run at full speed and hit him in the side. He's in pain, he's shaking and now has saliva hanging from his mouth (he normally doesn't)?
I would take him to the Vet cause he could have suffered a seizure