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#2:
Human demo of Halpike Dix shows the Right EYE with a tiny video inset of full body positioning.

It is hard to see, but the L ear is positioned down.
bppv.mp4

  1. Describe the nystagmus in the supine position.

  2. Describe the nystagmus when brought to sitting

  3. What is the diagnosis?
1. After a brief latency there is Upbeating and Left torsion.

This is followed by a pause, and then there a several beats of Left Horizontal nystagmus.  Since the left ear is down, (toward the earth), is is labeled Geotropic nystagmus (whereas beating away from the earth would be called Ageotropic)..

2. When brought back up to sitting it converts to Downbeating nystagmus.

3. Therefore it is Left Post SCC BPPV.
 
Also, there appears to be some involvement with the Left Horizontal canal as well.