A typical hangover peaks as blood alcohol returns to zero and then steadily improves over about a day; symptoms that get worse instead, such as shaking, sweating and anxiety, a worsening headache after a knock to the head, or a fever, point to something else. For hangover vs withdrawal, timing is the clue: withdrawal usually starts within 8 hours of the last drink, peaks at 24 to 72 hours and can be dangerous. Any of these lookalikes deserves medical advice, and some need 911.
Key takeaways
- Hangover symptoms peak when blood alcohol returns to about zero and can last 24 hours or longer, according to NIAAA.1
- Alcohol withdrawal symptoms usually begin within 8 hours of the last drink and peak by 24 to 72 hours; seizures, fever, severe confusion or hallucinations need 911.2
- CDC's concussion danger signs include a headache that gets worse and doesn't go away, repeated vomiting, slurred speech and one pupil larger than the other.3
- Slow breathing (fewer than 8 breaths a minute) or irregular breathing (10 seconds or more between breaths) after drinking can mean alcohol poisoning.4
How a normal hangover behaves
A hangover starts as blood alcohol approaches zero, peaks then, and fades. The direction matters more than any single symptom: a hangover should be easing as the day goes on.1
NIAAA lists fatigue, weakness, thirst, headache, muscle aches, nausea, stomach pain, vertigo, sensitivity to light and sound, anxiety, irritability, sweating and raised blood pressure; fever isn't on the list.1 See hangover symptoms and how long a hangover lasts.
| Possibility | Clues that point to it | What to do |
|---|---|---|
| Normal hangover | Improves through the day | Rest, water, food, time |
| Alcohol withdrawal | Regular heavy drinking, then stopping; shakiness, anxiety, sweating that build over 1 to 3 days | Medical advice; 911 for seizures, fever or hallucinations |
| Alcohol poisoning | Confusion, vomiting, seizures, slow or irregular breathing, can't be woken | Call 911; don't leave them alone |
| Concussion | A fall or knock to the head; headache that worsens, repeated vomiting, confusion | Emergency care for danger signs |
| Food poisoning or a stomach bug | Diarrhea, fever, others sick too | Fluids; a doctor for severe signs |
| Migraine | Throbbing one-sided pain, aura, lasting into a second day | Usual migraine plan; urgent care for red flags |
Alcohol withdrawal
Withdrawal happens when someone who has been drinking heavily on a regular basis stops or cuts back. Unlike a hangover, it tends to build after the last drink instead of fading, and it may quickly become life-threatening.2
Symptoms tend to start within 8 hours of the last drink, peak by 24 to 72 hours and may go on for weeks.2 They include anxiety, shakiness or tremor, irritability, sweating, a rapid heart rate, insomnia and nausea. Delirium tremens, the severe form, brings sudden confusion, fever, hallucinations and seizures. Call 911 for seizures, fever, severe confusion, hallucinations or an irregular heartbeat.
Next-day anxiety alone is common.5 But needing a morning drink to get going after heavy drinking is a warning sign on the WHO's alcohol screening test.6 Stopping after long, heavy drinking should be planned with a doctor, who can prescribe medicines that make withdrawal safer; NIAAA's Alcohol Treatment Navigator can help you find care.7 See what alcohol detox really means.
Alcohol poisoning
Alcohol poisoning isn't a bad hangover; it happens while alcohol is still high, and blood alcohol can keep rising after drinking stops.4 Signs include confusion, trouble staying conscious, vomiting, seizures, slow or irregular breathing, clammy skin, very low body temperature and bluish or pale skin. Call 911, don't leave the person alone, and roll them onto their side if they're lying down.4 More in signs of alcohol poisoning.
Concussion after a night out
Falls are easy to forget after drinking, and a concussion can share a hangover's headache and nausea. The clues are a head injury and symptoms that worsen.
CDC says adults need emergency care right away for a headache that gets worse and doesn't go away; weakness, numbness, poor coordination or seizures; repeated vomiting; slurred speech or unusual behavior; one pupil larger than the other; confusion or agitation; or being very drowsy or impossible to wake.3 If you can't remember the end of the night and have any of these, don't wait.
Food poisoning and stomach bugs
Diarrhea and fever point away from a hangover. CDC lists diarrhea, stomach cramps, nausea, vomiting and fever as the most common food-poisoning symptoms, starting anywhere from hours to days after eating.8
Norovirus usually starts 12 to 48 hours after exposure and clears within 1 to 3 days.9 If friends who shared the late-night food are sick too, it's probably not the drinks.
See a doctor for bloody diarrhea, diarrhea lasting more than 3 days, a fever over 102°F, or vomiting so often you can't keep liquids down.8
Migraine
Drinking too much alcohol can trigger migraine.10 Migraine pain is throbbing and usually one-sided, often with nausea and sensitivity to light, noise and smells; some people get an aura first, and attacks can last hours to days. See hangover headache.
Get help right away for a sudden, explosive or "worst ever" headache, one after a head injury, or one with fever, stiff neck, slurred speech, vision changes or weakness.11
Low blood sugar and other medical conditions
Low blood sugar. For people with diabetes on insulin or other glucose-lowering medicines, alcohol makes blood glucose harder to keep steady, especially without food, and can hide early symptoms of a low, such as shakiness and confusion.12 Eat when you drink.
Pancreatitis. Heavy alcohol use is a common cause. The main symptom is upper-belly pain that may spread to the back; severe or worsening belly pain needs care right away.13
Too much acetaminophen. Overdose can cause nausea, vomiting and upper-belly pain that's easy to mistake for a hangover; get help immediately.14 Acetaminophen plus alcohol can harm the liver, and NSAIDs plus alcohol raise the risk of stomach bleeding, so follow the label and ask a pharmacist. See pain relievers and alcohol.
When to see a doctor or go to the ER
Call 911 for signs of alcohol poisoning, a seizure, hallucinations or severe confusion, a head injury with a CDC danger sign, a sudden explosive headache, or someone you can't wake.4, 2, 3, 11
Get medical care the same day if symptoms are worsening, you have a fever over 102°F, bloody diarrhea or vomiting that stops you keeping fluids down, severe or worsening belly pain, shakiness and sweating after stopping regular heavy drinking, or you may have taken too much acetaminophen.8, 13, 14
What we don't know yet
There's no test for a hangover, so telling it apart from other conditions rests on timing and symptoms. Why some hangovers feel flu-like isn't settled; immune signals rise with hangover severity, but the link is correlational.15
Current US guidance is "Consume less alcohol for better overall health," and pregnant women, people in recovery and people on interacting medicines shouldn't drink at all.16 Hangovers impair coordination, so don't drive while hungover.1
Frequently asked questions
How do I know if it's withdrawal or a hangover?
A hangover follows a bout of drinking and eases as the day goes on. Withdrawal follows regular heavy drinking, usually starts within 8 hours of the last drink and builds over 1 to 3 days, with shakiness, anxiety and sweating. It can become dangerous: talk to a doctor, and call 911 for seizures, fever, hallucinations or severe confusion.
Can a hangover feel like the flu?
Yes. Fatigue, muscle aches, headache and sweating are all hangover symptoms. But fever isn't on NIAAA's list, so a real fever suggests an infection.
Is it a hangover or food poisoning?
Diarrhea, fever, and other people who ate the same food getting sick point to food poisoning or a stomach bug. See a doctor for bloody diarrhea, diarrhea for more than 3 days, a fever over 102°F or vomiting that keeps you from holding down liquids.
Can a hangover last 3 days?
NIAAA says symptoms can last 24 hours or longer, but a hangover should be improving. Symptoms that persist or build over two or three days suggest something else, such as withdrawal, an infection or a head injury, so get checked.
Sources
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). Hangovers. Updated December 2025. niaaa.nih.gov
- MedlinePlus (U.S. National Library of Medicine). Alcohol withdrawal. Reviewed January 1, 2025. medlineplus.gov
- Centers for Disease Control and Prevention. Symptoms of Mild TBI and Concussion. September 15, 2025. cdc.gov
- NIAAA. Understanding the Dangers of Alcohol Overdose. Updated December 2025. niaaa.nih.gov
- Rothman R, Hayley AC, Aitken B, Downey LA. A systematic review of the impact of the alcohol hangover upon negative affect. Drug Alcohol Rev. 2026;45(1):e70052. PubMed
- Babor TF, Higgins-Biddle JC, Saunders JB, Monteiro MG; World Health Organization. AUDIT: The Alcohol Use Disorders Identification Test. Guidelines for Use in Primary Care, 2nd ed. (WHO/MSD/MSB/01.6a). 2001. who.int
- NIAAA. Treatment for Alcohol Problems: Finding and Getting Help. Updated February 2025. niaaa.nih.gov
- Centers for Disease Control and Prevention. Food Poisoning Symptoms. Updated November 24, 2025. cdc.gov
- Centers for Disease Control and Prevention. About Norovirus. April 24, 2024. cdc.gov
- National Institute of Neurological Disorders and Stroke. Migraine. Last reviewed August 10, 2026. ninds.nih.gov
- MedlinePlus (U.S. National Library of Medicine). Headache. Reviewed October 27, 2025. medlineplus.gov
- National Institute of Diabetes and Digestive and Kidney Diseases. Low Blood Glucose (Hypoglycemia). Last reviewed July 2021. niddk.nih.gov
- National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & Causes of Pancreatitis. Last reviewed November 2017. niddk.nih.gov
- MedlinePlus (U.S. National Library of Medicine). Acetaminophen. Drug information, last revised October 15, 2025. medlineplus.gov
- van de Loo AJAE, Mackus M, Kwon O, et al.. The inflammatory response to alcohol consumption and its role in the pathology of alcohol hangover. J Clin Med. 2020;9(7):2081. PubMed
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2025–2030. Released January 7, 2026. realfood.gov (PDF)
- Substance Abuse and Mental Health Services Administration. SAMHSA's National Helpline. Accessed October 9, 2026. samhsa.gov
Published by Fuller Health, which makes After Party. This article is general information, not medical advice: talk to a doctor or pharmacist about your own health, medicines and drinking. Last reviewed October 9, 2026. How we research and write.