A hangover is the combination of negative mental and physical symptoms you experience after drinking alcohol, and it kicks in as your body finishes processing the alcohol out of your system. Symptoms typically hit full force the morning after heavy drinking and can last up to 24 hours. If you woke up feeling rough after a night out and you’re wondering whether what you’re feeling is actually a hangover, here’s what to look for.
The Core Physical Symptoms
The most recognizable hangover symptoms are physical. You’ll likely notice some combination of fatigue, weakness, thirst, headache, muscle aches, nausea, stomach pain, and sensitivity to light and sound. Sweating, dizziness, and increased blood pressure are also common. Not everyone gets every symptom, and the mix can vary from one drinking episode to the next, but the overall pattern of feeling physically drained and uncomfortable is the hallmark.
Thirst is one of the earliest and most reliable signals. Nearly everyone with a hangover reports it. But here’s something worth knowing: drinking water doesn’t actually fix a hangover the way most people assume. A recent review of the evidence found that dehydration and hangovers are two separate consequences of drinking that happen to occur at the same time. People who drank water during or after alcohol consumption saw only a modest effect on preventing next-day symptoms, and drinking water during the hangover itself didn’t change how severe it felt. So while thirst is a clear sign you’re hungover, quenching it won’t make the rest of the symptoms disappear.
The Mental and Cognitive Signs
A hangover isn’t just physical. The mental symptoms can be just as disruptive, sometimes more so. Trouble concentrating is reported by roughly 96% of people experiencing a hangover, making it the single most common symptom. It also has an outsized impact on how well you function: concentration problems interfere with cognitive tasks far more than they affect mood or physical ability.
Sleepiness and feeling tired dominate the experience for most people. You may also notice irritability, a general sense of emotional unease, or lower alertness than usual. Anxiety and depression do occur during hangovers, but they’re the least common and least severe symptoms. If you’ve heard the term “hangxiety” for post-drinking anxiety, it’s real, but it affects a smaller portion of people than headaches or brain fog do.
Decision-making and organizational thinking can also take a hit. Research has shown that managerial-type skills, like planning and prioritizing, tend to suffer during a hangover. This is part of why a hangover can make a workday feel nearly impossible even when you’re not nauseous or headachy.
Why You Feel This Way
Your body treats alcohol like a mild toxin, and the hangover is essentially the aftermath of your immune system responding to it. When your liver breaks down alcohol, the process generates harmful byproducts that trigger inflammation throughout your body. Blood levels of inflammatory markers, including proteins your immune system releases when fighting infection, rise significantly after drinking and correlate directly with how bad the hangover feels. The more inflammation, the worse your symptoms.
Interestingly, the old theory that a toxic intermediate chemical produced during alcohol metabolism is the main culprit doesn’t hold up well. Studies have found no significant link between blood levels of that byproduct and hangover severity. Instead, alcohol itself appears to directly provoke the inflammatory response. At four hours after drinking, blood alcohol levels (not the byproduct) were associated with elevated inflammatory markers.
Alcohol also disrupts your sleep in ways you can feel the next day. Even if you slept a full night, the quality was compromised. Drinking reduces total sleep time, sleep efficiency, and the amount of time spent in REM sleep, the deep, restorative phase your brain needs. Your heart rate also runs higher overnight. One study found average nocturnal heart rate jumped from about 56 beats per minute on a placebo night to 65 after drinking. So even if you got “enough” hours of sleep, your body didn’t get the recovery it needed, which feeds directly into next-day fatigue and brain fog.
When Symptoms Start and How Long They Last
Hangover symptoms begin as your blood alcohol concentration drops toward zero. This is a key detail: you’re not hungover while you’re still drunk. The two states don’t overlap. For most people who drink in the evening, this means symptoms emerge in the early morning hours and are in full effect by the time you wake up.
Most hangovers resolve on their own within 24 hours, though severity varies widely. You don’t need to have been heavily intoxicated to get one. Research has documented meaningful hangover symptoms in people who drank as few as two beers, with estimated peak blood alcohol levels well below the legal driving limit. Your individual biology, how fast you metabolize alcohol, how hydrated you were to begin with, whether you ate, and what you drank all play a role.
Hangover vs. Something More Serious
A standard hangover is unpleasant but not dangerous. What you want to watch for are signs that cross into alcohol poisoning territory, which is a medical emergency. The key differences:
- Confusion beyond normal grogginess, where the person can’t track a conversation or doesn’t know where they are
- Seizures
- Slow breathing, fewer than eight breaths per minute
- Irregular breathing, with gaps of more than 10 seconds between breaths
- Blue-tinged or pale skin
- Low body temperature
- Loss of consciousness, especially if the person can’t be awakened
These symptoms typically appear while someone is still intoxicated or very shortly after they stop drinking, not the next morning. A person who is unconscious and can’t be woken up is at risk of dying and needs emergency care immediately.
It’s also worth distinguishing a hangover from alcohol withdrawal, which affects people who drink heavily and regularly. Withdrawal symptoms can look similar (anxiety, trembling, sweating) but tend to be more severe, can include hallucinations or dangerous seizures, and occur because the body has become dependent on alcohol to function normally. If you only drink occasionally and you’re feeling rough the morning after, that’s almost certainly a hangover, not withdrawal.
A Simple Self-Check
If you drank alcohol last night and woke up with some combination of headache, thirst, fatigue, nausea, trouble concentrating, and sensitivity to light or sound, you’re hungover. There’s no blood test or formal threshold required. Researchers assess hangovers by simply asking people to rate how they feel across those symptoms on a scale of 0 to 10, and the clinical definition is straightforward: negative mental and physical symptoms after a single episode of drinking, starting when alcohol leaves your system.
The severity can range from barely noticeable to completely debilitating, and it doesn’t always scale neatly with how much you drank. Some people get significant hangovers from moderate amounts of alcohol. Others drink more and feel relatively fine. Genetics, body composition, sleep quality, and the inflammatory response your immune system mounts all factor in. If you’re consistently surprised by how bad you feel after what seems like a reasonable amount of alcohol, that’s just how your body processes it.