Can a dog go into shock after a near miss accident?

My 18 month old Shih Tzu/ Pomeranian was almost hit by a car yesterday. I took him to the vet and they ured me that he was ok, but he is acting very strange. He has had diarrhea all day, he won't bark to go out, and I gave him a bath to clean his backside up and he just laid in my arms for about 30 minutes. He is normally a happy active dog who is completely housebroken, so I am very concerned about this behavior.