My 1 1/2 year old pug is unable to put weight on his hind legs.?

My dog was fine last night when he came in and went to his crate for the night. This morning I let him out and he was unable to get up. He just scooted on the floor. I picked him up and carried him out to eat and go potty. He did eat all his food. After that he was able to walk to the yard and go potty. When he does walk his legs are shaking. I carried him in and he is laying down now. Toby has had no previous health problems and is very active.