If x-rays don't show an abnormality, it's likely a tear/sprain/strain soft tissue-type injury and it hurts, sometimes pretty badly depending upon what's the injury actually is. I'd give him his meds until he can successfully bear full weight on it again after his enforced rest period is over. Remember, dogs can feel pain & the only way they can tell us is by how they act. A shaking, uncertain-acting, quiet dog is probably one that is hurting and needs a break from the discomfort/pain. He feels vulnerable from his injury(dogs are genetically programmed to be stoic, not show pain/weakness if at all possible) and is holding back to protect himself and heal.
It's okay for a dog to be drowsy from medication if injured so don't shy away if your vet prescribed it unless he vomits wildly, goes berserk or something drastic like that. I'd crate rest him, reassure him and allow him pain relief and time to heal and when he's not hurting & vulnerable, you'll likely see his former personality and full weight bearing return.
__________________  Jeanie and Tibbe One must do the best one can. You may get some marks for a very imperfect answer: you will certainly get none for leaving the question alone. C. S. Lewis |