A concussion doesn’t always look dramatic. There’s no bleeding, no visible bruise on the brain, and more than 90 percent of concussions happen without any loss of consciousness. That makes identifying one tricky, because the signs are often subtle and can show up hours or even days after the injury. Knowing what to look for across several categories of symptoms is the most reliable way to catch a concussion early.
You Don’t Have to Black Out
The biggest misconception about concussions is that you have to “get knocked out” for it to count. In reality, the vast majority of people who sustain a concussion never lose consciousness. A concussion is a functional brain injury caused by a force that makes the brain shift or rotate inside the skull. This disrupts normal cellular activity, triggering a cascade of ionic imbalances and energy demands that the brain then has to repair. You can walk, talk, and seem perfectly fine while this process is underway.
Because loss of consciousness is rare, relying on it as your main indicator means you’ll miss most concussions. Instead, pay attention to how you feel, think, and behave in the minutes, hours, and days after a head impact or any blow to the body that transmits force to the head.
Physical Symptoms to Watch For
The most common and recognizable physical sign is a headache, often described as pressure in the head. Beyond that, look for:
- Dizziness or balance problems, including feeling unsteady on your feet
- Nausea or vomiting, especially in the first hours after injury
- Sensitivity to light or noise, where normal environments feel overwhelming
- Blurred or double vision
- Fatigue or very low energy, out of proportion to your activity level
These symptoms can appear right away or develop gradually. Some people feel fine immediately after a hit and then notice a worsening headache or dizziness a few hours later. The CDC notes that symptoms can shift over the course of recovery, too. Early on, headaches and nausea tend to dominate. A week or two later, emotional and sleep-related symptoms become more prominent.
Thinking and Memory Changes
Cognitive symptoms are sometimes harder to notice because they don’t cause pain, but they’re a hallmark of concussion. The person may feel mentally foggy or “groggy,” like their brain is operating through a thick layer of cotton. Thinking feels slower than usual. Concentration becomes difficult, and short-term memory can slip, with trouble recalling conversations or what happened just before the injury.
If you’re trying to identify a concussion in someone else, ask simple questions: What day is it? What were you doing before this happened? Can you repeat back a short list of words? Struggling with orientation questions or immediate recall is a strong indicator. Formal sideline assessments used in sports test exactly this, asking the date, month, year, and time, plus having the person recall a ten-word list and recite months in reverse order.
Emotional and Sleep Disruptions
Concussions affect mood in ways that people often don’t connect to the injury. Increased irritability, feeling more emotional than usual, sudden sadness, or unusual anxiety can all signal a concussion. These emotional shifts happen because the brain’s ability to regulate mood is temporarily impaired.
Sleep changes are equally telling. Some people sleep far more than normal, while others develop insomnia or have trouble falling asleep. Either direction is significant. If someone who normally sleeps well suddenly can’t fall asleep, or if they’re sleeping 12 to 14 hours and still feel exhausted, that pattern fits a concussion profile.
Symptoms Can Be Delayed
One of the trickiest aspects of identifying a concussion is timing. Some symptoms appear immediately, but others don’t surface for hours or even days. This is why it’s important to monitor anyone who has taken a significant hit for at least 24 to 48 hours after the injury, even if they initially seem fine. A headache that starts six hours later or concentration problems that show up the next morning still point back to the original impact.
Because of this delayed onset, re-evaluate how you feel multiple times after an injury rather than making a one-time judgment in the moment.
Red Flags That Need Emergency Care
Most concussions are manageable, but certain symptoms indicate a more serious brain injury that requires immediate medical attention. The Sport Concussion Assessment Tool (SCAT6), the current standard used internationally, flags these as red-flag signs:
- Seizure or convulsion
- Repeated vomiting
- Severe or worsening headache that doesn’t ease up
- Double vision
- Weakness, tingling, or burning in more than one limb
- Neck pain or tenderness
- Increasing restlessness, agitation, or combativeness
- Deteriorating awareness, where the person becomes harder to wake or less responsive over time
Any of these symptoms after a head injury warrants a trip to the emergency room. They can indicate bleeding or swelling inside the skull, which is a medical emergency.
What About Checking the Pupils?
You’ve probably seen someone shine a flashlight into an injured person’s eyes in movies. Pupil checks can indicate brain injury, but they’re far less reliable than most people assume. A difference of more than 1 millimeter between pupils can suggest a problem, but research from the Brain Trauma Foundation found that a single measurement of pupil asymmetry is neither highly sensitive nor specific for identifying a brain lesion. Up to 1 millimeter of natural asymmetry between pupils is completely normal.
In the field, without controlled lighting and proper tools, pupil exams are even less reliable. A fixed, dilated pupil that doesn’t react to light is a serious warning sign, but the absence of pupil changes doesn’t rule out a concussion. Rely on the broader symptom picture instead.
How Professionals Assess Concussions
There is no single blood test or brain scan that definitively diagnoses a concussion. CT scans and MRIs typically look normal after a concussion because the injury is functional, not structural. Instead, clinicians use multi-part assessment tools.
The SCAT6, updated following the 6th International Conference on Concussion in Sport in 2022, is recommended for use in the first 72 hours to one week after injury. It combines a 22-symptom checklist with cognitive screening (orientation questions, word recall, digits backward), a neurological exam, balance testing across three stances, and a timed heel-to-toe walking test. A newer companion tool, the SCOAT6, covers the subacute phase between 3 and 30 days post-injury for ongoing evaluation.
Vestibular and ocular motor screening (VOMS) tests five areas related to balance and eye movement: smooth visual tracking, rapid eye movements, the ability to focus on a near point, balance-vision coordination, and sensitivity to visual motion. Provocation of symptoms during any of these tests is a strong indicator of concussion.
Identifying a Concussion in Young Children
Toddlers and young children can’t describe a headache or brain fog, so you have to watch their behavior. Look for excessive crying or fussiness that’s hard to console, loss of interest in favorite toys or activities, unsteadiness when walking or crawling, changes in eating or sleeping patterns, and vomiting. A child who seems unusually drowsy, won’t stop crying, or loses skills they previously had (like balance or coordination) after a fall or collision needs evaluation.
Recovery Timeline
The most recent international consensus data puts average return-to-sport time at about 20 days across all age groups, with return to school or normal learning averaging around 8 days. Current guidelines recommend a graduated return-to-activity approach with two phases: a treatment and rehabilitation phase where light, symptom-tolerated aerobic exercise is encouraged, followed by a return-to-sport phase. During early recovery, mild symptoms (rated 0 to 2 out of 10 on a pain scale) and brief symptom flare-ups lasting less than an hour are considered acceptable during gentle activity.
Complete rest is no longer the standard advice. Early physical activity and aerobic exercise at a tolerable level are now considered effective therapeutic interventions. For people with persistent dizziness, headaches, or balance problems, targeted rehabilitation focusing on neck and vestibular function is recommended.