As a scientist and an engineer I couldn’t grasp how this condition I have is so… analog. Everyone just says “Oh a crystal got into your vestibular system”. And I think, “why is it so much worse some days than others?” How can I feel 95% ok like I do now with no real lasting vertigo but just little tinges of vertigo when I move my head fast? Either the crystal is there or it isn’t, based on how it’s been described to me.
Why isn’t BPPV exactly the same each time? Sometimes an attack will be so violent that you vomit, and other times it’s just a very tiny, momentary spin when looking up at the sky or bending over. The answer is very simple: it depends on the number of crystals that are moving. These crystals are tiny, like chalk powder. They’re normally attached to a gravity sensor in the ear, but if they get into a spinning sensor, the semicircular canals, vertigo can start. In order to cause symptoms they need to act like a plunger in the narrow canal as they move. One crystal can’t do that. It takes a cluster, and the larger the grouping, the more severe the symptoms.
(From Overcoming Positional Vertigo by Carol Foster MD)
Often when a spell starts, it’s because a large clump of crystals has entered the canal. After doing maneuvers, most of these leave. If you still feel a tiny bit of vertigo when looking straight up, though, it means you still have a few crystals in there and need to do more maneuvers. Everyone probably has a few crystals moving around in the canals, but not enough to cause symptoms. If you do maneuvers the first time you feel any vertigo, no matter how small, it can help keep too many from building up and setting off a major spell.