A hangover feels like a combination of exhaustion, nausea, headache, and a general sense of being unwell that can closely resemble a mild flu. Symptoms typically begin once your blood alcohol level drops back toward zero and can last up to 24 hours. The experience varies from person to person, but most hangovers share a recognizable set of physical and mental symptoms driven by several overlapping processes in your body.
The Physical Symptoms
The most common hangover sensations include extreme tiredness and weakness, thirst and dry mouth, headache and muscle aches, nausea or vomiting, dizziness, shakiness, sweating, and a fast heartbeat. Some people describe it as feeling “hit by a truck,” and that’s not far off from what’s happening inside your body. Multiple systems are stressed at once: your stomach lining is irritated, your brain chemistry is rebalancing, your immune system is inflamed, and you’re dehydrated.
The headache is one of the most recognizable parts. As your body breaks down alcohol, it produces a compound called acetate, which triggers a buildup of a chemical called adenosine in the brain. That adenosine appears to increase pain sensitivity, which is why your head pounds and why light and sound can feel unbearable. This sensitivity to light and sound mirrors what people with migraines experience, and for similar chemical reasons.
Why Your Stomach Feels Wrecked
Alcohol directly irritates and inflames your stomach lining. It weakens the protective mucus barrier that normally shields the stomach wall from its own digestive acids. The result is a gnawing or burning pain in your upper belly, waves of nausea, and sometimes vomiting. That queasy, unsettled feeling can linger for hours, and eating may make it better or worse depending on the person. For some people, the stomach discomfort is the dominant hangover symptom, overshadowing everything else.
The Flu-Like Feeling
One of the more surprising aspects of a hangover is how much it resembles being sick. The muscle aches, fatigue, and general malaise aren’t just from dehydration. Your immune system actually mounts an inflammatory response to alcohol. Studies have found elevated levels of inflammatory markers like C-reactive protein and certain signaling molecules (the same ones your body releases when fighting an infection) during a hangover. This inflammation, combined with oxidative stress, is now considered one of the primary drivers of how terrible you feel.
Alcohol also disrupts the integrity of your intestinal lining, creating what researchers describe as a “leaky gut.” This allows immune cells and bacterial compounds to enter the bloodstream, further fueling the inflammatory response. Through the connection between the gut and the brain, this inflammation contributes to the mental fog and low mood that come with a hangover, not just the body aches.
Why You Feel So Exhausted
Dehydration plays a role here. Alcohol suppresses a hormone that helps your kidneys retain water, so you lose more fluid than you take in. That mild dehydration contributes to thirst, fatigue, and headache. But dehydration alone doesn’t explain the bone-deep tiredness of a hangover.
A bigger factor is disrupted sleep. Alcohol initially acts as a sedative, helping you fall asleep faster and pushing you into deep sleep during the first half of the night. But during the second half, the effect reverses. You wake up more often, cycle between sleep stages erratically, and experience fragmented REM sleep. Even if you were in bed for eight hours, the quality of that sleep was poor. You wake up feeling like you barely slept at all, because in a meaningful sense, you didn’t.
Hangover Anxiety and Mental Fog
Many people wake up after drinking with a sense of dread, restlessness, or free-floating anxiety, sometimes called “hangxiety.” This isn’t just guilt about what you did the night before (though that can play a role). It has a clear biological cause.
While you’re drinking, alcohol enhances the activity of your brain’s calming system and suppresses the chemicals that make you feel anxious. You feel relaxed and uninhibited. But once alcohol wears off, your brain overcorrects. It dials down the calming signals and ramps up the anxiety-producing ones, trying to restore its normal balance. The result is that you feel more anxious than you did before you started drinking. If you can’t remember parts of the night, the psychological uncertainty amplifies that unease.
Alongside the anxiety, you’ll likely notice trouble concentrating, slower thinking, and difficulty with memory. When alcohol crosses into the brain, it triggers inflammatory responses that directly impair cognitive function and mood. This is why a hangover can feel mentally cloudy and emotionally flat, like trying to think through a fog while feeling vaguely sad or irritable for no specific reason.
How Long It Lasts
Hangovers generally last about 24 hours, though symptoms tend to peak in the morning and gradually improve throughout the day. The timeline depends on how much you drank, how quickly you drank it, whether you ate beforehand, and your individual biology. Some people feel mostly recovered by the afternoon. Others feel off for an entire day.
Your body processes alcohol through two steps: first into acetaldehyde (a toxic compound that contributes directly to hangover symptoms), then into harmless acetic acid. How fast your body completes that second step matters. Some people, particularly many people of East Asian descent, have a slower-acting version of the enzyme responsible for clearing acetaldehyde. This means the toxic intermediate lingers longer, producing more intense symptoms including facial flushing, nausea, and headache.
Why Some Drinks Feel Worse
Not all hangovers are created equal. Darker spirits like bourbon, brandy, and whiskey tend to produce more severe hangovers than lighter drinks like vodka, even at the same amount of alcohol consumed. The reason comes down to congeners, which are byproducts of fermentation that give darker drinks their color and flavor. One key congener is methanol, which your body breaks down into formaldehyde, a compound that produces its own set of hangover symptoms on top of what alcohol itself causes.
Red wine and dark spirits have the highest methanol concentrations, while beer and vodka have the lowest. Studies have found that hangover severity scores are significantly higher after bourbon compared to vodka at the same blood alcohol level. People with sulfite sensitivity may also get headaches specifically from wine. So the type of drink genuinely matters, not just the quantity.