A hangover shows up in a predictable cluster of physical, behavioral, and cognitive signs that are hard to hide. Someone who drank heavily the night before will typically look unwell, act differently than usual, and struggle with basic mental tasks. The symptoms usually begin once blood alcohol levels drop back toward zero and can persist for up to 24 hours. Here’s what to look for.
The Physical Signs You’ll Notice First
The most visible giveaway is how someone looks. Bloodshot, red eyes are one of the earliest and most obvious markers. Alcohol causes blood vessels in the eyes to swell, sometimes to the point of bursting, leaving the whites visibly irritated. You may also notice puffiness around the eyes and face, a result of dehydration pulling fluid into surrounding tissues. Their pupils may seem slow to react to changes in light.
Beyond the eyes, a hungover person often looks pale or slightly flushed, sweaty, and generally worn down. They’ll frequently reach for water or other drinks because alcohol suppresses the body’s ability to retain fluid, leaving them intensely thirsty. If they mention a headache, that’s one of the most commonly reported hangover symptoms, driven by both dehydration and the inflammatory byproducts of alcohol metabolism.
Stomach trouble is another telltale sign. Alcohol directly irritates the stomach lining and ramps up acid production, so someone dealing with a hangover may feel nauseous, complain of stomach pain, skip meals, or make frequent trips to the bathroom. In more severe cases, vomiting is part of the picture. Sensitivity to light and sound is also common, so you might notice them wincing at bright screens, squinting outdoors, or asking to turn down music.
How Their Behavior Changes
A hungover person rarely acts like themselves. The most frequently reported mood shifts include increased anxiety, irritability, and emotional flatness. Research on hangover mood changes has consistently found that people experience lower alertness, higher fatigue, and a general sense of physical discomfort that colors everything they do. They may seem withdrawn, short-tempered, or unusually quiet in situations where they’d normally engage.
Apathy is reported by over 80% of people during a hangover, which looks like a lack of interest in conversations, plans, or responsibilities. About a third of hangover sufferers also report feeling depressed, and roughly one in five experience noticeable anxiety. These aren’t subtle shifts. If someone who’s normally upbeat seems flat, distracted, and easily annoyed the morning after a night out, that combination of mood changes is a strong signal.
Cognitive Slowdowns
One of the most reliable ways to tell if someone is hungover is by how their thinking changes. Concentration problems are reported by nearly 96% of people experiencing a hangover, making it the single most common cognitive symptom. You might notice them struggling to follow a conversation, losing their train of thought, or needing things repeated.
Research measuring brain performance during hangovers found significant impairments across several types of mental tasks. Hungover participants made roughly 22% more errors when asked to switch between tasks, and their working memory (the ability to hold and update information in real time) was notably worse, with error rates increasing by nearly 45% on short-term memory tests. Their ability to maintain focus on a goal also dropped, with more than twice the errors on sustained attention tasks compared to their sober baseline. In practical terms, this means a hungover person may seem scatterbrained, forgetful, slow to respond, or unable to manage more than one thing at a time.
Movement and Coordination Clues
Even after someone is no longer intoxicated, alcohol’s effects on balance and coordination can linger. Studies using precise body-sway measurements show that alcohol disrupts the brain’s ability to maintain stable posture, particularly side-to-side balance. A hungover person may seem slightly unsteady on their feet, grip surfaces for support, or move more carefully than usual. These effects are subtle compared to active intoxication but noticeable if you’re paying attention, especially when they close their eyes (standing in an elevator, for example) or navigate uneven ground.
Fine motor skills like typing, writing, or handling small objects may also be slightly off. This isn’t dramatic stumbling; it’s more like a general physical sluggishness, as if their body is running at 70% capacity.
Vital Signs That Change
Some hangover signs aren’t visible but are felt by the person experiencing them. Heart rate and blood pressure both increase during a hangover because the heart has to work harder as the body processes alcohol’s aftereffects. Someone might mention their heart feels like it’s racing, or they may seem winded from activities that wouldn’t normally bother them. Sweating more than usual is another common report, even in cool environments.
Trembling or shaking hands, while less common than headache or fatigue, does appear on clinical hangover assessments as a recognized symptom. If you notice someone’s hands shaking slightly when they pick up a cup or try to write, it can be a sign of a more severe hangover.
Timing Tells You a Lot
Context matters. Hangover symptoms begin once blood alcohol concentration falls back toward zero, which for most people means they hit hardest in the morning or early afternoon after a night of heavy drinking. Symptoms typically peak within the first several hours after waking and gradually improve over the course of the day, though they can last a full 24 hours in some cases.
If someone seemed fine at midnight but looks terrible at 9 a.m., with red eyes, low energy, a headache, irritability, and trouble concentrating, the timeline alone narrows the possibilities. The combination of physical, behavioral, and cognitive signs appearing together after a plausible drinking occasion is the clearest indicator. Any one symptom in isolation could have other explanations, but the full cluster showing up on a predictable morning-after timeline is unmistakable.