My guess would be that there is a brain tumor or he had a stroke to the brain stem. These, along with Vestibular disease, are the most common causes of head tilt in dogs.
Vestibular is a disease where we usually don't know the cause. It comes on suddenly and then goes away on it's own over 7-14 days. If he was incoordinated and then got back to normal other than the head tilt, I would call it Vestibular. Some dogs will have a residual head tilt. It doesn't cause any issues and they live normally.
If he has had chronic or progressive neurologic signs, then I would think of a brain stem tumor or stroke to the brain stem. You really need an MRI to see these. Sometimes a CT will show it, but strokes are not easy to see on CT. That is where an MRI is needed.
The treatment for tumors is radiation therapy or meds to bring down the swelling around the brain. Ultimately, they are fatal tumors. If a stroke, we can see some improvement over 2-4 weeks. After that time, the neurologic function remaining is usually as good as they'll ever get.
Let me know if you have any other questions.