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When the patient with horizontal canal BPPV is quickly brought from the sitting to the supine position, a mild horizontal nystagmus may appear, attributed either to ampullofugal movement of otoconia in the horizontal canal (geotropic type), triggering nystagmus toward the unaffected ear, or in cases of cupulolithiasis (apogeotropic type) to ampullopetal deflection of the cupula, resulting in nystagmus directed toward the affected ear.
