We had the same problem a few years ago and last year again in the course of two months twice. The second time was between Christmas and the New Year. That is scary. We watch him all the time and anytime he makes different sounds, I check his eyes, touch his ears, touch his lower back to see how he reacts. In cases like this, you really have to go immediately to the vet, and they always could see us immediately.
Good luck to Logan. He'll get better.