There are many viruses that are attracted to nervous tissue (neurotropic) and so can attack the brain and nerves. The inner ears are each served by nerves that exit directly from the brain, and so can be affected by viruses that cause brain inflammation (encephalitis), and infection of the lining of the brain (meningitis). There are many viruses that can do this. Common neurotropic viruses include the enteroviruses (for example, polio and stomach flu); herpesviruses that cause cold sores; influenza, and the viruses that cause measles and mumps. Recently COVID-19 has been linked to brain inflammation and dizziness.
Many of these viruses are known to cause infection of the nerves leading to the ears, which are all branches of the eighth cranial nerve: the cochlear nerve that serves hearing, the superior vestibular nerve serving the anterior or front half of the labyrinth, and the inferior vestibular nerve which serves the posterior or back half of the labyrinth. Infections of these nerves can affect hearing, balance, and control of eye movements.
Vestibular neuritis is a type of severe vertigo disorder in which hearing remains normal. This means that in the classic form, the cochlear nerve is not involved. Usually it is just one branch of the 8th nerve, the superior vestibular nerve, that is affected. That nerve controls the horizontal semicircular canal, which is the most-needed rotation sensor in the head, since most head movements in people are horizontal or side to side. It also controls the anterior canal, which senses up and down head rotation, and the utricle, a gravity sensor.
It often follows other signs of a viral infection, like a cold or stomach upset. It starts with severe vertigo, and the room is usually seen to spin continuously. This can worsen over several hours and continue for a day up to several days before gradually tapering off. During the peak vertigo, there is a tendency to drift to one side when walking. Nausea, vomiting, sweating and anxiety are usually experienced. Sometimes the floor will appear to be tilted, a sign that the utricle is involved.
The longer the symptoms last, the slower recovery is likely to be. If the room spinning disappears in a day or two, then any remaining milder dizziness is likely to go away completely. This usually indicates a milder amount of damage to the ear. If the spinning lasts a week, there may be a residual dizziness. This indicates that there has been a larger loss of function in the ear. Damage to the nerve to the ear is permanent, but recovery or improvement of the symptoms will usually occur. Some people have positional vertigo (BPPV) after having had vestibular neuritis, and can use maneuvers to treat this.
If you experience this disorder, you can still return to normal. You can compensate gradually to a partial or even total loss of balance function in the ear, but it can take weeks to months before you feel fully normal. You can speed this up by taking long daily walks, moving your head to stimulate the dizziness, and practicing home exercises as seen in this video.