Up-beating torsional
Posterior-canal BPPV — the commonest positional vertigo.
What the animation does not show. The animation holds a steady up-beating torsional beat for clarity. It does not reproduce the latency, the build-and-fade, or the fatigue on repeat — those are timing features you judge at the bedside, not values this looping teaching clip measures.
Provoked by the Dix-Hallpike after a short latency: up-beating with a torsional component toward the down ear, building then fading inside a minute, and weaker on each repeat. Treated with the Epley, not referred.
The pattern is a sequence, not a steady beat: latency, then crescendo-decrescendo. After the head is dropped into the Dix-Hallpike position the eyes stay quiet for a short latency — a second or a few — then the nystagmus builds, peaks, and settles within a minute. Repeat the maneuver and each response is often weaker. Be careful with that last one: the AAO-HNS guideline's diagnostic criteria are three, and fatigability is not among them — torsional up-beating nystagmus with vertigo on Dix-Hallpike, a latency period, and resolution within 60 seconds (Bhattacharyya 2017, Table 6). The Barany Society calls fatigability a common finding, not a criterion (von Brevern 2015). It supports the impression; it does not make or break it.
The direction ties to the mechanics. The vertical component beats up and the torsional component beats toward the dependent, down ear, matching displaced otoconia stimulating the posterior canal. Because it is a benign, mechanical problem, the answer is a repositioning maneuver — the Epley — rather than a referral (Bhattacharyya 2017).
The mirror of this is the reason to hesitate. A positional beat that is purely vertical (downbeat, especially with no torsional component), that switches direction with gaze rather than with position, or that fits no single canal's plane is not posterior-canal BPPV — those features point central (Bhattacharyya 2017; von Brevern 2015). A horizontal beat that reverses as the head is rolled to each side is different: that is horizontal-canal BPPV, still peripheral (see Horizontal direction-changing).
Source: AAO-HNS BPPV clinical practice guideline (Bhattacharyya 2017).