This is a reasonably common condition, usually of older dogs. Onset is sudden: head is usually to one side and there is loss of balance. It is very frightening to observe but recovery is the norm although the dog may be quite disturbed for a few days. The clincher for diagnosis is a sign called nystagmus which means rhythmic twitching of the eyes from side to side or up and down. Get your pet checked quickly to be sure there is nothing more drastic wrong with the central nervous system.