BPPV (Benign Paroxysmal Positional Vertigo)

Loose Marbles in a Curved Tube

Imagine a clear curved plastic tube (the semicircular canal) partially filled with honey (the endolymph fluid). Inside the tube sits a spring-loaded gate (the cupula) that normally only opens when you spin the whole tube in a circle—the honey sloshes and pushes the gate, which sends a signal. Now drop loose marbles (the otoconia) into that tube. When you tilt the tube gently forward, the heavy marbles roll downward, plowing through the honey and creating a wave that pushes the gate even though you are not spinning—a false alarm. The gate sends the same 'spinning' signal it always does, so your brain believes you are rotating and makes your eyes jerk to compensate, even though you are nearly still. The moment the marbles settle at the bottom and stop rolling, the honey calms, the gate stops getting pushed, and the false signal vanishes—but the marbles are still there, waiting for the next tilt to roll again.