Benign paroxysmal positional vertigo

The semicircular canals normally detect rotation, not gravity

The semicircular canals of the inner ear detect rotational head movement through the inertia of fluid (endolymph) moving past a sensory cupula. Separately, the utricle and saccule contain otoconia (tiny calcium carbonate crystals embedded in a gel) that detect linear acceleration and head position relative to gravity. These two systems normally work independently: the canals should only respond to rotation, and the otoconia should stay confined to the utricle.