system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we get the 'spins' after drinking?

There are times I don't even think I'm drunk but as soon as I Iay down I'm suddenly on a roller coaster. Why do we get the spins and why do they sneak up on us when (while standing) we don't feel dizzy ?
gpt
Your sense of balance is based on 3 systems. Your vestibular system in the inner ear, your sense of touch and proprioception, and sight. Your brain takes those 3 inputs and together creates a sense of balance. You need at least two active and working correctly at least, your brain can function without one, though it can take a few weeks to adjust if your vestibular nerves are cut. 

Ok, but then what causes the spins? Alcohol creates fluid density changes in the inner ear, so it's messing with the vestibular system. But you've not got the spins yet right? You might be a bit off balance but you're doing ok. So what if we took the other two systems out of commission as well. The spins creep up on you once you turn off the lights and close your eyes (losing sight), and lay on a soft thing on the floor instead of feet firmly planted on the ground (losing some touch/proprioceptive information). Now we've got incorrect and unusual information coming from the inner ear due to the fluid changes, and the other two systems aren't sending much useful information either. Welcome to spin-city. 

If you want to avoid the spins, you should not smoke and drink. If you're cool though, and still want to avoid the spins, open your eyes, look at static things (so not your ceiling fan), and plant a foot firmly on the floor. Get those other 2 systems working.