Dog suddenly arching back in pain?

we took our 5 yr old cocker spaniel to the vet today because soon after our walk he all of a sudden was in a lot of pain- arching his back, couldnt get comfy sitting or laying down, and was shaking. the vet couldnt pinpoint his pain nd were waiting on bloodwork results. our dog didnt swallow anything he shouldnt have... he has started having seizures: 2 seizures in 6 months...and has looked like hes had hip or lower back pain starting this past yr like he lays and sits down slower than he used to - we also found a mouse had gotten in his food bag and i was reading about lepto? but he hasnt had bleeding fever vommiting or diarhea... anyone have any ideas of what it could be since the vet couldnt tell us today?