Many of us have experienced this at least once; after having one too many drinks, you seem to lose your balance and start having difficulty walking in a straight line. You might even become nauseated in a particularly severe case.

So why is it that your head starts spinning after consuming alcohol? We'll attempt to answer this conundrum in this article.

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Vestibular system

To understand anything about this phenomenon, we need to take a look at our vestibular system. The vestibular system consists of three tubes, called semicircular canals and the otolith located in your inner ear.

The otolith is responsible for detecting linear acceleration. The semicircular canals, on the other hand, are responsible for detecting rotational movements. They are very precise and can pick up the tiniest actions.

The semicircular canals are filled with a fluid called endolymph and contain a small membrane (called the cupula) that holds tiny hair cells which are capable of detecting whether the membrane is moving.

When you make a quick spinning movement, the fluid inside the semicircular canals lags behind the actual movement and rushes by the cupula membrane. The tiny hair cells detect the spin and send a signal to the brain conveying that acceleration is taking place. This detection can happen in 3 dimensions as we have three semicircles in each inner ear, all working together.

A schematic overview of the vestibular system. Each inner-ear has one of these. - Image Credit: Designua via Shutterstock / Edited by Universal-Sci - (click to enlarge)

Your right vestibular organ is a little more sensitive to movements to the right, so when you turn to the right, there is a heightened activity in the right vestibular organ, while a decrease in activity is noticed in your left vestibular organ. If you turn the other way, you get the opposite effect. Your brain looks at the difference between both organs, from which it can then deduce what is happening.

Only susceptible to a change in speed

The vestibular system is mainly sensitive to a change in speed (acceleration). You can easily portray this by putting someone on a swivel chair and spin them around with their eyes closed while holding their head straight.

As the chair slowly accelerates in its spinning movement, the person sitting on the chair is able to assess what is happening. But after acceleration has stopped and the chair is spinning at a constant rate, their vestibular system will get used to the motion.

The person in the chair will probably not get nauseated as long as the speed stays constant; however, when you ask them to put their chin on their chest, the situation changes drastically. The semicircular channels concerned with vertical movement are now getting stimulated. With their head bowed down, the person in the chair suddenly will get the sensation of tumbling forward instead of spinning in a circle, losing a sense of what is up and down.

Why does the world keep spinning for a while after you yourself stopped spinning?

Another interesting phenomenon happens after you stop spinning the chair. Even though the chair is motionless, the person in the chair may still feel the sensation of the world is spinning around. This has to do with inertia; the fluid in their vestibular system remains restless for a while and has to settle down to get a proper sense of movement.

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Interestingly, the ffact that the vestibular system gets accustomed to a constant speed can pose a problem for pilots as it is difficult to detect very slow turns. Pilots are therefore trained to trust their instruments rather than their own sense of movement.

The semicircular canals are not sensitive to translation (movements that advance in a straight line and do not make a rotational shift). That's because the density of the cupula membrane is the same as that of the fluid around it.

Imagine an aquarium with metal balls at the bottom. If you move the aquarium back and forth, those metal balls will move around the bottom of the aquarium. However, if you were to put in balls made out of something with the same density as the water, they won't move. A similar situation befalls the density ratio of fluid in the semicircular canals and the membrane.

So what happens with your vestibular system when you drink alcohol?

So what happens if you start drinking alcohol? About 10 minutes after drinking an alcoholic drink, that alcohol has entered the cupula membrane through the bloodstream. As you may know, alcohol is lighter than water; it is also lighter than the fluid in your semicircular canals (endolymph).

Suddenly the membrane starts floating as it has become lighter than the fluid in your semicircular canals because it has absorbed the lighter alcohol. So if, for example, you were to lie on your side at that moment, it would bend and tell the brain that you are spinning. This is what makes you nauseated.

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After about 6 to 7 hours, the alcohol will be mixed with the fluid in your semicircular canals and will once again be at equilibrium with the membrane.

Wait for yet another few hours, and the situation will change again. Now the alcohol has been entirely removed from the membrane but still remains mixed with the fluid in your semicircular canals.

You will experience the opposite effect from before, as the membrane is now heavier than the fluid in your semicircular canals it will bend the other way. This is what you experience during a hangover.

Why does your hangover feel less severe when you start drinking again?

If you were to take another glass of alcohol during your hangover, the membrane would start to absorb alcohol once again, making it lighter, changing towards an equilibrium again.

So, to put it in different words, an important property of the semicircular canals is that they are not sensitive to gravity. The fluid inside has the same density as the membrane. However, the moment you start drinking alcohol, you make the system sensitive to gravity because you are changing the density of the different components at a different speed.

Finally, there is a link between your vestibular system and what is called your autonomic nervous system. The autonomic nervous system is responsible for things like your heart rate and blood pressure. It is also connected to the brain's vomiting center. If you have a particularly strong connection in that area, you will get nauseated more easily.

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