BPPV, or Benign Paroxysmal Positional Vertigo, is a common cause of vertigo, or a false sense of spinning. It is fairly common among adults, with increased incidence as you age. It usually comes on without an apparent reason, however can occur after a head trauma or after spending time in a head tipped back position (such as in a dentist chair). Usually you will first notice symptoms when turning over in bed or when sitting up from bed in the morning.
The spinning sensation occurs due to a mechanical problem in the peripheral vestibular system of the inner ear. This system has calcium crystals called otoconia that sit on a gel-like substance and are sensitive to gravity, as well as three semicircular canals filled with fluid that are oriented in three different planes. In a normal vestibular system, the fluid in the canals moves when your head moves. This displaces hair cells and sends a message to the brain to tell it that your head is moving. Sometimes the otoconia crystals become dislodged into the fluid and give your brain a false signal that your head is moving when it’s not. This results in a spinning sensation, or vertigo.