Very worrying. One striking symptom of Vestibular Disease is rapid eye movement. The eyes go zinging left to right like the dog is watching a high speed tennis match. They sort of roll around too, a bit like the guy in a cartoon who is drunk. Head tlit is also a striking symptom. But of course not all dogs show all the same symptoms. Also, VD generally comes on quickly, lasts for several weeks THEN disappears quickly.
If he is better that's good but you want to know what it was, the how, what, why, when so you can ensure no repeats. Sometimes we just don't get that. Good luck.