Nystagmus secondary to BPPV has the following nearly pathognomic characteristics: A latency period of 5 to 10 sec Usually, vertical (upward-beating) nystagmus when the eyes are turned away from the affected ear and rotary nystagmus when the eyes are turned toward the affected ear Nystagmus that fatigues when the Dix-Hallpike maneuver is repeated In contrast, positional vertigo and nystagmus related to CNS dysfunction have no latency period and do not fatigue.