You spin around several times and stop.
Your feet are planted.
The room keeps moving.
The problem is not the room. It is the balance system inside your inner ear.
Your inner ear contains motion sensors
Deep inside the ear are fluid-filled structures called semicircular canals.
When your head turns, the fluid inside them moves. That movement bends tiny sensory structures that send information to the brain about rotation.
This balance system is also involved in motion sickness, where the brain has to reconcile movement signals from different senses.
The trouble starts when you stop
Your body can stop almost instantly.
The fluid has momentum.
For a short time after you stop, fluid inside the canals can keep moving and continue bending the sensory structures.
Your inner ear is effectively saying:
“We are still turning.”
Your eyes and the rest of your body are saying:
“No, we are definitely standing still.”
The brain gets conflicting information
Your brain normally combines signals from the inner ear, eyes, muscles, and joints to understand movement and position.
When those messages disagree, your sense of orientation can become temporarily distorted.
That is why the world may seem to rotate even though you know logically that it is stationary.
Why does the dizziness fade?
The fluid gradually settles.
The sensory structures return toward their resting positions.
Now the signals from your ears, eyes, and body agree again.
The room stops appearing to move.
Why do some people get dizzy more easily?
People differ in how sensitive their balance systems are.
The speed of spinning, number of turns, head position, fatigue, illness, medications, and other factors can affect the response.
Someone who is already prone to motion sickness may notice the sensation more strongly.
Is all dizziness caused by the inner ear?
No.
Dizziness can describe several different sensations and can have many causes.
Dehydration, blood-pressure changes, medications, migraines, illness, and neurological problems can all produce dizziness.
The brief spinning sensation after deliberately turning in circles is a specific and usually harmless example.
So after you stop spinning, the world is not still moving.
Your body stopped.
The fluid in your inner ear just did not get the memo quite as quickly.
And that’s the short explanation.
Related explanations: Why do we get motion sickness?, Why do we get pins and needles?, and Why do your ears ring?