There is a syndrome, variously referred to as peripheral vestibular syndrome (the current "preferred name"), geriatric vestibular syndrome and idiopathic vestibular syndrome. This disorder is more common in older dogs and thus the name geriatric vestibular syndrome -- but it can occur in middle aged dogs, too, so the name was changed. Idiopathic just means "happens for no known cause" -- so it is a good name but not the preferred one. It does sum up the situation well, though. For some reason dogs can suddenly develop vestibular disease. The problem seems to be due to inflammation in the nerves connecting the inner ear to the cerebellum (which controls balance and spatial orientation). It usually lasts between a couple of days and three weeks. A few dogs have residual signs beyond this time, such as a head tilt. This disease normally affects dogs that seem normal up until the signs appear. Then there is sudden loss of balance with many dogs unable to even stand up. Rythmic eye motion known as nystagmus is usually present. Dogs may be nauseous from the "sea sickness" effect of vestibular disease. Most dogs will not eat or drink unless hand fed or given water by hand because they have a hard time with the fine motor movements necessary to eat or drink from a bowl. As long as they are nursed through this condition almost all dogs will recover. There is no known treatment. Some dogs do have relapses but most do not.
Peripheral vestibular disease can be confused with anything that will cause cerebellar damage or inner ear disease. Inner ear infections are probably the most common cause of similar symptoms and if recovery does not progress satisfactorily it is a good idea to do whatever testing seems necessary to rule out inner ear problems, such as ear examination and X-rays. Cancer affecting the cerebellum, the peripheral nerves to the cerebellum or the inner ear can cause similar signs. In golden retrievers lymphoma is a common cancer problem that can cause CNS signs. Trauma is a possible problem that could be confused with peripheral vestibular syndrome if brain damage occurs. Granulometous meningoencephalitis (GME). Infarcts (blood clotting leading to lack of circulation in part of the brain) occur in some dogs. If the damage to the brain is minimal then recovery may occur quickly. If the damage is severe, recovery may not occur at all. I do not know the incidence of infarcts affecting the brain in dogs but I think it is pretty low.
Even when dogs do not recover fully from peripheral vestibular syndrome they normally have a good life. They adjust to residual problems like head tilts and do not seem all that bothered by them. If progress towards recovery is not evident, then the other disorders mentioned above need to be considered.