A hangover is your body’s reaction to drinking enough alcohol to reach intoxication, and its symptoms are surprisingly consistent: headache, nausea, fatigue, thirst, dizziness, and difficulty concentrating. Symptoms typically begin as your blood alcohol level drops toward zero and can last 24 hours or longer. If you drank heavily the night before and woke up feeling some combination of these, you almost certainly have a hangover.
The Core Symptoms
Researchers have identified 12 hallmark hangover symptoms through a standardized severity scale used in clinical studies. They are: fatigue, clumsiness, dizziness, apathy, sweating, shivering, confusion, stomach pain, nausea, difficulty concentrating, heart pounding, and thirst. You don’t need all 12 to have a hangover. Most people experience a cluster of four or five, with fatigue, thirst, and headache being the most common.
What you might not expect is the mental fog. Hangovers measurably impair working memory, sustained attention, and reaction time. A study testing cognitive performance during hangovers found that people completed tasks significantly more slowly as hangover severity increased, and that short-term memory, long-term memory, and psychomotor speed are the mental functions hit hardest. If you’re struggling to focus, losing track of conversations, or feeling mentally “slow,” that’s a textbook hangover symptom, not just tiredness.
Why You Feel This Way
Several things are happening in your body at once, which is why hangovers feel like more than just one problem.
Dehydration. Alcohol suppresses the hormone that tells your kidneys to hold onto water. Drinking roughly four standard drinks causes your body to flush out 600 to 1,000 mL of water beyond what you took in. That’s up to a full quart of extra fluid loss, which drives the thirst, headache, and dizziness.
Stomach irritation. Alcohol directly inflames the stomach lining and ramps up acid production while slowing digestion. This is why your stomach hurts, why you feel nauseous, and why eating sounds unappealing even though food would help.
Toxic byproducts. Your liver breaks alcohol down in two steps. The intermediate product between alcohol and the harmless end result is a reactive, toxic compound that causes flushing, rapid pulse, sweating, and nausea. Most people clear it efficiently, but its effects can linger into the hangover window even after it’s been fully processed. Some people carry a genetic variant that makes them clear this compound slowly, which is why they get visibly flushed and feel sick after even small amounts of alcohol.
Blood sugar drops. Alcohol metabolism interferes with your liver’s ability to produce glucose. Low blood sugar contributes to the shakiness, weakness, and irritability that come with a hangover.
The Anxiety Component
If you feel anxious, restless, or emotionally fragile the morning after drinking, that’s not just guilt or regret. It has a biological basis. Alcohol enhances the activity of your brain’s calming system while suppressing its excitatory system. After hours of drinking, your brain compensates by dialing up excitatory activity and dialing down the calming response. When the alcohol leaves your system, that rebalancing overshoots, leaving your nervous system in a hyperactive state. The result is anxiety, irritability, a racing heart, tremors, and a general sense of dread that people sometimes call “hangxiety.” This is the same mechanism behind clinical alcohol withdrawal, just a much milder version of it.
When Symptoms Start and How Long They Last
Hangover symptoms begin as your blood alcohol concentration drops and peak right around the time it hits zero. For most people, that means symptoms are worst in the morning after a night of drinking, roughly 6 to 8 hours after your last drink. From that peak, symptoms gradually fade but can persist for a full 24 hours or longer depending on how much you drank.
The pattern matters for identification. If you feel worst immediately after drinking, you’re still intoxicated. A hangover is what comes after: the slow, grinding discomfort that sets in once the alcohol itself is gone. One distinguishing feature is that hangovers primarily slow you down (slower reaction times, sluggish thinking), while intoxication impairs accuracy and judgment.
Does the Type of Alcohol Matter?
It does, but less than you might think. Darker liquors like bourbon, whiskey, and red wine contain higher levels of compounds called congeners, which are byproducts of fermentation. Studies comparing bourbon (high congener content) to vodka (virtually no congeners) found that bourbon produced noticeably worse hangovers. But the alcohol itself was the far stronger predictor of hangover severity than the type of drink. Switching to “cleaner” spirits may take the edge off, but it won’t prevent a hangover if you drink enough.
Hangover or Something More Serious
A standard hangover is miserable but not dangerous. Alcohol poisoning is. The critical difference is that a hangover happens after your body has processed the alcohol, while alcohol poisoning happens when there’s still a dangerous amount in your system. If someone is showing these signs, the situation is a medical emergency:
- Inability to wake up or stay conscious
- Slow breathing (fewer than 8 breaths per minute) or gaps of 10 seconds or more between breaths
- Seizures
- Bluish or pale skin, or skin that feels clammy and cold
- Mental confusion or stupor beyond normal grogginess
- No gag reflex (risking choking on vomit)
You do not need to see all of these symptoms before acting. A person who has passed out from alcohol and cannot be woken can die. Vomiting while unconscious is one of the most common ways alcohol poisoning becomes fatal.
For a typical hangover, the signs that you’re recovering are straightforward: your thirst becomes manageable, nausea fades, your thinking sharpens, and your energy returns. There’s no shortcut to this process. Your body needs time, water, food, and rest to finish clearing the inflammatory and metabolic aftermath of heavy drinking.