"The best hangover remedy of all time is two packets of Emergen-C and quart of water before you pass out. If you're drinking, it's the ultimate hangover cure. It's basically electrolytes, so it prevents dehydration. Plus, it prevents you from bloating three days after you drink."
It's dehydration that causes the headache, but also, in the body and kidneys it throws off what's called your aldosterone levels. If you become dehydrated and you pass out, you wake up and your tongue is stuck the top of your mouth. You look in the mirror, and you're super lean, but then what happens the next three days? You get on the scale, and you're up 6 pounds and you're puffy. When you're aldosterone levels get thrown off, you actually uptake sodium for the next few days. Because your body goes, "I don't know when you're going to have water again. You were just severely dehydrated for 12 hours." So it just uptakes sodium at this rapid rate. Everything you eat, the sodium sticks. So, the water and Emergen-C are really important."