Benign Paroxysmal Positional Vertigo (BPPV)
In benign paroxysmal positional vertigo, calcium carbonate crystals from the utricle fall into one of the semicircular canals — most often the posterior canal — and stimulate positional vertigo.
In the slow phase of the nystagmus, from the observer’s (or examiner’s) perspective:
The anterior canals produce upward movements.
The posterior canals produce downward movements.
The right-side semicircular canals stimulate movements in a clockwise direction.
The left -side semicircular canals stimulate movements in a counterclockwise direction.
See the Dix-Hallpike Maneuver for bedside evaluation of BPPV.