Labyrinthitis is an inflammatory disorder of the inner ear, or labyrinth. Clinically, this condition produces disturbances of balance and hearing to varying degrees and may affect one or both ears. Bacteria or viruses can cause acute inflammation of the labyrinth in conjunction with either local or systemic infections. Autoimmune processes may also cause labyrinthitis. Vascular ischemia may result in acute labyrinthine dysfunction that mimics labyrinthitis.
It can be triggered by viral or bacterial infections, as well as air travel and diving. It usually fully resolves after six weeks or so. It's thought to affect around 35 million people each year.
The exact mechanism which leads to the condition have not been identified.
More info UK NHS