If you drank heavily last night and woke up feeling awful this morning, you almost certainly have a hangover. The symptoms are distinctive: some combination of headache, nausea, thirst, fatigue, dizziness, stomach pain, and a racing heart. Most hangovers hit full force the morning after drinking, once your blood alcohol level drops to or near zero, and clear up on their own within 24 hours.
That said, not every post-drinking misery is the same. Here’s how to recognize what you’re dealing with, what’s actually happening in your body, and when the symptoms point to something more serious.
The Nine Core Symptoms
Researchers who study hangovers use a validated checklist called the Acute Hangover Scale, which captures the nine symptoms people most reliably report. They are: a general feeling of being hungover, thirst, tiredness, headache, dizziness or faintness, loss of appetite, stomachache, nausea, and a racing heart. You don’t need all nine to have a hangover. Most people experience a cluster of three to five, and the intensity varies from mild to completely incapacitating.
The most common trio is headache, thirst, and fatigue. If those three showed up together after a night of drinking, that’s a hangover. Nausea and stomach pain tend to appear when the drinking was heavier or involved darker liquors. A racing heart catches some people off guard because they don’t associate it with alcohol, but it’s a well-documented hangover symptom caused by your body’s inflammatory and dehydration response.
When Symptoms Start and How Long They Last
Hangover symptoms begin as your blood alcohol level falls, not while you’re still drunk. This is why you can feel fine at midnight and terrible at 7 a.m. For most people, symptoms peak in the morning and fade over the course of the day. The full window can stretch up to 24 hours, though moderate hangovers often lift by the afternoon.
The timing helps distinguish a hangover from other problems. If you feel sick while you’re still actively intoxicated, that’s the alcohol itself affecting you, not a hangover. And if symptoms persist well beyond 24 hours or worsen on the second day, something else may be going on.
Why You Feel So Tired
One of the most frustrating hangover symptoms is bone-deep exhaustion, even after sleeping seven or eight hours. This happens because alcohol wrecks your sleep quality from the inside. While it may help you fall asleep faster, it fragments your sleep throughout the night, causing your brain to briefly wake up and interrupt your sleep cycle over and over. Each of those micro-awakenings pulls you back into light sleep and cuts into your REM sleep, the deep, restorative stage that’s essential for feeling rested, thinking clearly, and regulating your mood.
So even a full night in bed after drinking leaves you running on low-quality sleep. That’s why hangover fatigue feels different from normal tiredness. It often comes with brain fog, irritability, and trouble concentrating, all consequences of lost REM sleep.
What’s Actually Happening in Your Body
A hangover isn’t one thing. It’s several overlapping problems hitting you at once. Alcohol is a diuretic, meaning it makes you urinate more than the volume of fluid you’re taking in. That leads to dehydration, which drives the thirst, dry mouth, and headache. At the same time, alcohol irritates the lining of your stomach, triggering nausea, stomach pain, and loss of appetite.
Your body also has to break down the alcohol itself, and that process produces a toxic intermediate called acetaldehyde. Until your liver clears it, this compound contributes to the general feeling of malaise. On top of all this, alcohol triggers an inflammatory response throughout your body, which can cause muscle aches, difficulty concentrating, and that vague sense of being unwell that’s hard to pin to any one symptom.
Why Some Drinks Cause Worse Hangovers
Not all alcohol punishes you equally. Darker drinks like bourbon, brandy, cognac, red wine, dark whiskey, and tequila contain higher levels of chemical byproducts called congeners. These are created during fermentation and aging, and they include compounds like methanol, which your body breaks down into formaldehyde and formic acid. The more congeners in your drink, the worse the hangover tends to be.
Clear drinks like vodka, gin, white wine, light rum, sake, and light beer have much lower congener levels. If you had several glasses of bourbon and feel significantly worse than a friend who drank the same amount of vodka, the congener difference is a likely explanation. Of course, total alcohol consumed still matters most. Enough of any drink will produce a hangover.
Hangover vs. Alcohol Poisoning
A hangover is miserable but not dangerous. Alcohol poisoning is a medical emergency, and the two can look different in important ways. With a hangover, you’re conscious, aware of your symptoms, and functional enough to be searching the internet about it. With alcohol poisoning, the situation is far more severe.
The warning signs of alcohol poisoning include:
- Confusion beyond normal grogginess
- Slow or irregular breathing
- Repeated vomiting, especially while unconscious or semi-conscious
- Pale, bluish, or cold skin
- Seizures
- Inability to stay conscious
These symptoms typically appear while a person is still intoxicated or shortly after they stop drinking, not the next morning. If someone you’re with shows any of these signs, that’s a 911 call, not a wait-and-see situation. A person can die from alcohol poisoning, and they cannot “sleep it off.”
How to Tell It’s Not Something Else
A handful of other conditions overlap with hangover symptoms, which can create confusion. Food poisoning causes nausea, vomiting, and stomach cramps, but it typically also involves diarrhea and sometimes fever, and it doesn’t depend on alcohol consumption. A migraine triggered by alcohol can feel similar to a hangover headache, but migraines often come with sensitivity to light and sound that’s more intense than what a typical hangover produces, and they may affect only one side of the head.
The simplest diagnostic question is: did you drink enough alcohol last night to cause this? If you had one glass of wine with dinner and woke up with a headache and nausea, that’s probably not a hangover. Look for other explanations. If you had five or six drinks and woke up with the classic cluster of thirst, headache, fatigue, and an unsettled stomach, you have your answer.