I had this test when I was in my 20's. I had terrible vertigo when I was younger.
I have had several "attacks" since then. When the test was done, it showed my left vestibular nerve was not functioning.
The thought then was that occasionally it woke up and interfered with my adjustment (in the brain) and caused havoc.
The repositioning bit...is what is used for benign positional vertigo.
This sort of explains it:
His might be slightly different, but the principle is the same.
I had a terrible time with metformin and vertigo, 6mos into using it. I had to stop it in fact. It really gave me a terrible time with the vertigo.
When I had my thyroid fixed, most of the acute attacks ended...except for that metformin incident!