Spin on the spot and stop suddenly: your body is stationary, yet the room may seem to keep turning. The cause is not the scene in front of you but the way the inner ear measures rotation.
Each inner ear contains three fluid-filled semicircular canals arranged roughly at right angles. When the head starts turning, the canal walls move immediately while the endolymph briefly lags because of inertia. This deflects the gelatinous cupula and bends sensory hair cells, sending a signal that the head is rotating. During steady rotation, the fluid gradually catches up and the signal weakens even though the person is still turning.
When you stop abruptly, the pattern reverses. The canal walls stop, but the fluid briefly continues moving and pushes the cupula in the opposite direction. The vestibular system therefore signals rotation while vision and bodily sensation report that you are stationary. The brain receives conflicting information, creating the impression that the room is still spinning and sometimes producing rhythmic eye movements.
The fluid is not circling inside the ear for a long time. The effect comes from brief mechanical motion followed by sensory recalibration. The ordinary sensation after spinning usually fades quickly. Recurrent or persistent vertigo without spinning is a different matter and cannot be diagnosed from this playground mechanism.
https://www.nidcd.nih.gov/health/balance-disorders
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