Last night sure was fun, but this morning your tongue feels like sandpaper. Your aching head is too heavy to lift from the pillow. You desperately want a glass of water, but the kitchen seems miles away. Your gut is churning. You might throw up. You might have horrible diarrhea. Maybe both.

We all know how to get here: too many generous happy hour pours. But why do we feel so awful and what can we do about it? Science has fewer firm answers than we'd like.

Though alcohol has been a recreational drug of choice for thousands of years, scientists have yet to pinpoint the exact mechanism that makes us drunk. Of the many thousands of scholarly papers on alcohol, only a few hundred touch on the hangover.

"We know a lot about the long-term effects of alcohol on the body," says Dr. Vinay Sundaram, a hepatologist who studies alcoholic liver disease. "What's happening in the body while you're drinking and when you're hungover—that's more of a mystery."

It's become a more popular research topic in the last decade. Newer studies are finding what we thought we knew about hangovers and how to cure them is largely the stuff of urban legend. But like many urban legends, they sometimes have some grains of truth.

Legend: Dehydration is the problem behind hangovers.

Just drink water between every drink. The symptoms of dehydration and hangovers are similar, so they must be related.

Science says: There's no evidence that dehydration is the culprit.

While the symptoms are similar, it doesn't hold up to scientific scrutiny. Electrolyte levels in hungover people and control groups are roughly the same. And those with lower electrolyte levels don't seem to have worse hangovers.

Staying hydrated with water is still a smart move. So even if it's a myth, drink water.

Legend: Dark liquor means a worse hangover than vodka.

Science says: This may true.

One study compared a group of younger adults (ages 21-33) who drank enough bourbon to get drunk to a group who drank vodka. The drinkers in the study became equally impaired and had the same amount of difficulty sleeping. Both got hangovers. But the bourbon drinkers were significantly more miserable.

Legend: Hangovers are related to a toxin released when your liver processes alcohol.

When your body breaks down ethanol, it creates a particularly nasty byproduct called acetaldehyde. Studies in the early 2000s tied it to many hangover symptoms.

Science says: Results unclear.

More recent studies found this may be a dead end. Because acetaldehyde is so toxic, the body quickly changes it into a more stable compound called acetate. While acetate can trigger a headache, hangover symptoms seem to be at their worst when acetaldehyde levels are low.

Legend: A hangover is your immune system freaking out and creating an inflammatory response.

While "freaking out" isn't the scientific term, it's an apt description of the flurry of immune system activity that's the focus of some studies.

Science says: This seems to be true.

A team of  researchers noticed hangovers are often accompanied by elevated levels of cytokines, the messaging system for our bodies' immune responses.

When cytokines get busy, the immune system begins firing, and that can cause inflammation. It also causes a host of other hangover-like symptoms: headaches, chills, fatigue, nausea, stomach upset. And cytokines can mess with memory formation, meaning they might also account for alcohol-related lapses in memory.

It's still being studied, but if inflammation is indeed the underlying mechanism, an anti-inflammatory pain reliever might help ease a hangover.

Legend: The "hair of the dog" will stop your hangover.

Drink a beer in the morning, and that will relieve your hangover.

Science: Nope.

The origin of the term "hair of the dog" comes from the 1500s, when medical practitioners of the day thought you could cure rabies by drinking a potion made with the hair of the dog that bit you. It worked about as well to cure rabies as having a drink in the morning works to cure a hangover.

Which is to say, it doesn't.

You may feel a little buzzed after yet another drink, which might feel comparatively better, but the other symptoms will come back. So you're only delaying the inevitable.

Want to avoid a hangover? Keep the alcohol to a minimum, or even consider skipping it entirely. Moderate drinking is considered 1 drink a day for women and 2 drinks a day for men.

"Moderation," says Dr. Sundaram. "It may be a predictable ending to the story, but we know it's what works."