Poor Lightning is having a tooth pulled as we speak. I had noticed that his breath was particularly bad, so I suspected something in his mouth was infected. Turns out he had a cracked tooth! Poor baby--no telling how long it's been hurting him. I feel like a bad mom.
Lightning is back from the vet and already sound asleep. Everything went well, although it was a big tooth they pulled (they gave it to me to keep--should I put it under Lightning's pillow tonight?). But they said his blood tests looked great, as did his EKG (he's 12, so that was a huge relief to hear). So we're both resting comfortably now.