When the year ends, many of us take the time to reflect by getting utterly obliterated. But what’s actually going in your body and brain after two or three or five drinks?

Alcohol, technically “ethanol,” is a simple chemical with powerful neurological effects. There’s still some disagreement as to how exactly alcohol makes you feel the way it does. Scientists do know that it interferes with parts of the nervous system’s cells in a few different centers in your brain. But why do you lose your sense of balance?

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Balance is controlled by a surprisingly complex system. Inside each of your inner ears, three hair-lined tubes form a sort of three-dimensional matrix. Fluid fills the tubes, and the movement of the fluid on the hairs sends signals to your brain to tell you how you’re oriented in space.

But alcohol doesn’t just enter your brain—it enters your bloodstream and your inner ears, too. It changes the blood’s density, causing the inner ear to change shape and the three-dimensional matrix to deform. This changes what the hairs perceive and messes with the signals that your brain receives. That can cause you to feel like the room is spinning.

If you drink alcohol faster than your body can process it, there’s a host of other things you might need to worry about. Of course there’s the euphoria, but there’s also the bad judgment, slurred speech, nausea, and eventually blackout, coma, and death. So don’t drink that much. Also, don’t get behind the wheel of a car, you know?

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But it’s New Year’s Day, the perfect time for some reasoned drinking, thinking, and contemplation. So why not think about science?

Correction: A previous version of this article incorrectly described how alcohol influences the balance system in the inner ear, as pointed out by commenters. It has been updated, and we regret the error.