If you've ever woken up feeing so terrible that you momentarily convince yourself that the massive party you dreamed about last night was real, you know that you don't actually have to be hungover to feel hungover. The general malaise of a hangover — headache, brain fog, fatigue, soreness, nausea — is not only attributed to a night of excess boozing. The fundamental cause of most hangovers is dehydration, which doesn't just come from drinking alcohol.
According to Christen Cupples Cooper, Ed.D., R.D., a professor at the College of Health Professions at Pace University, hot weather, sports, illnesses that cause diarrhea and vomiting, and simply not taking in enough liquids can lead to varying degrees of dehydration, which can make you feel hungover. "Mild dehydration can lead to brain confusion, fatigue, dizziness and irritability," Cooper tells Bustle, also likely describing many of your mornings.
Sure, there are lots of other things that can make a night of drinking lead to a particular kind of garbage morning — the sugar content of the drinks, and the time and state in which you went to bed — but depriving your body of useful liquids is the number one culprit of a hangover in most cases. According to internist Dr. Nate Favini, M.D., medical lead of Forward, a preventive primary care practice, alcohol is a diuretic, "which means it can cause you to urinate more often and lose more fluid from your body," contributing to a dehydrated state. As for why alcohol has this effect on the body, internist Dr. Sunitha D. Posina, M.D., says that "alcohol triggers the suppression of a hormone called Vasopressin," aka, a hormone that tells your kidneys to release more sodium and water into your urine, which leaves less water in your body, which you need for healthy blood flow. "Other contributors to hangovers include your body’s inflammatory response to alcohol, stomach irritation, and poor sleep quality."
Thirst often comes after the point at which we missed the hydration boat.
There are, of course vary degrees of dehydration, but even a moderate case prohibits the body's ability to get blood, nutrients, and oxygen to your organs. "As you become more dehydrated, your sodium levels rise and the brain perceives that you need water, which will leave you feeling thirsty. Next, you might begin to experience lightheadedness and tunnel vision when you stand up," Dr. Favini says. Some less obviously related symptoms of dehydration are dry skin, sunken eyes, dry mouth, leg cramps, any constipation, Dr. Posina adds. The more serious dehydration gets, the more sick you will feel. "With severe dehydration, circulation to your kidneys will begin to fall, your liver may become inflamed and muscles can start to break down. Eventually, you can pass out and lose consciousness," Dr. Favini explains.
While thirst is typically a good indicator that your body needs water, it's not always the case. "While it seems logical that they body would signal thirst to prompt us to drink, thirst often comes after the point at which we missed the hydration boat," Cooper says. Meaning, by the time you're headed to the sink, you might already have some mild to moderate signs of dehydration going on in the body.
A good indicator of being hydrated is when your urine is clear. The darker and more yellow it is, the more concentrated it is, which typically points to a lack of water content. So long as you don't feel considerably confused, sleepy or near unresponsive, Dr. Favini says you can easily correct your hydration levels by drinking water, or drinking something with electrolytes and some sugar in it, like a Gatorade, because it helps your body absorb water faster. To avoid dehydration in the first place, Cooper suggests drinking eight to 10 cups of liquids a day; if that feels intense for you, it's OK to work your way up slowly over time.
Christen Cupples Cooper, Ed.D., R.D., a professor at the College of Health Professions at Pace University
Dr. Nate Favini, M.D., internist
Dr. Sunitha D. Posina MD, a board-certified physician of Internal Medicine in Stony Brook, New York.