Hi Katie! Sometimes the displaced otoconia sneak onto the other side of the cupula (the “anterior arm” of the semicircular canal). In that case, they are not stuck to the cupula but cause ageotropic/apogeotropic nystagmus. This type of canalithiasis is relatively rare, though it does constitute around 50% of people with ageotropic nystagmus. It’s probably more in the vestibular weeds than you need for the NCS exam – knowing big picture for BPPV is more critical!
