Signs of a Concussion: Symptoms and When to Seek Help

After a head injury, some signs are an emergency

Call 911 or go to the nearest emergency room if, after a bump, blow, or jolt to the head, a person has any of these: loss of consciousness (even briefly), a headache that keeps getting worse or is severe, repeated vomiting, a seizure or convulsion, slurred speech, weakness, numbness, or poor coordination, one pupil larger than the other, confusion, agitation, or unusual behavior, unusual drowsiness or cannot be woken, clear fluid or blood draining from the nose or ears, or symptoms that worsen over time. These can signal bleeding in or around the brain or a skull fracture. Have an especially low threshold to seek care for infants and young children, adults over 65, and anyone on blood thinners or with a bleeding disorder. When in doubt, get it checked.

A hard hit to the head during a car accident, a fall on the ice, or a collision on the playing field can all cause a concussion — and the signs of a concussion are not always obvious. You do not have to lose consciousness to have one. In fact, the large majority of concussions happen with no blackout at all, according to the CDC. That means many concussions go unrecognized because people assume they are fine if they did not pass out. Knowing what to look for — both immediately and in the hours or days afterward — can be the difference between a smooth recovery and a prolonged struggle. This article is educational and is not a substitute for evaluation by a clinician. For more on conditions that affect millions of Americans, visit our medical conditions guide.

What Is a Concussion?

A concussion is a mild traumatic brain injury (mTBI) caused by a bump, blow, or jolt to the head — or a hit to the body that makes the head and brain move rapidly back and forth. This sudden movement causes the brain to shift or twist inside the skull, setting off temporary chemical and functional changes in brain cells. The National Institute of Neurological Disorders and Stroke (NINDS) classifies concussions as “mild” traumatic brain injuries, though “mild” refers to the low risk of life-threatening bleeding, not to how the symptoms feel — which can be significant and disruptive.

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Concussions are common. Falls are the leading cause of traumatic brain injury overall — especially in young children and older adults — while motor vehicle crashes, assaults, being struck by or against an object, and sports and recreation account for much of the rest. Estimates of sports- and recreation-related concussions in the United States run into the millions each year, but the true number is uncertain because so many are never reported or diagnosed. The practical takeaway is not the exact figure: it is that concussions are frequent, often missed, and worth recognizing early.

Immediate Signs of a Concussion

Some concussion symptoms appear within seconds or minutes of the injury. Others develop gradually over hours. Recognizing the immediate signs matters because it prompts proper evaluation and, in athletes, immediate removal from play.

Headache is the most common symptom, reported by the great majority of people with a concussion. It often feels like pressure or a dull ache that worsens with physical or mental effort. Dizziness and balance problems are common right after impact. Confusion or feeling “foggy” is a hallmark sign — the person may seem dazed, answer slowly, ask the same question repeatedly, or struggle to remember what happened just before or after the injury.

Nausea and vomiting can occur, particularly in the first few hours; a single episode is common, but repeated vomiting is a red flag for a more serious injury and needs emergency evaluation. Sensitivity to light and noise frequently accompanies the headache. Blurred or double vision affects many people and usually resolves within days. Ringing in the ears (tinnitus) can occur. A brief loss of consciousness happens in a minority of concussions, but when it does, it is a definitive sign that the head took a significant hit — and any loss of consciousness warrants prompt medical assessment.

Delayed Signs That Appear Hours or Days Later

Not all concussion symptoms show up immediately. Some emerge 24 to 72 hours after the injury, which is why monitoring in the days following a head impact is so important. Symptoms that worsen over hours — rather than gradually improving — should trigger an urgent re-check, because a delayed bleed (such as a subdural hematoma) can develop after an initially normal exam.

Difficulty concentrating and memory problems often become apparent when the person tries to return to work, school, or daily routines. Tasks that were previously easy — reading, following conversations, managing a to-do list — may feel overwhelming. Sleep disruption is common and takes multiple forms: difficulty falling asleep, sleeping more than usual, or sleeping less than usual.

Mood changes including irritability, anxiety, sadness, and emotional volatility frequently emerge in the days after a concussion. People may cry more easily or lose their temper over minor frustrations. A deep, persistent fatigue that does not improve with rest is one of the most limiting delayed symptoms. Word-finding trouble, slower processing speed, and feeling mentally “slow” round out the cognitive symptoms that may not surface until the person tries to resume normal activities. If low mood, hopelessness, or anxiety become severe or persistent after a concussion, treat that as a reason to seek care — see our overview of the symptoms of depression.

Signs of a Concussion in Children

Children and toddlers cannot always describe their symptoms, which makes concussion recognition harder for parents. Look for behavioral changes rather than verbal reports. A child who becomes unusually cranky, will not stop crying, refuses to eat or nurse, loses interest in favorite toys, or appears listless may have a concussion.

The CDC’s HEADS UP program advises watching for unsteady walking, excessive drowsiness, and vomiting in young children after any head impact. School-aged children may complain of headaches, have trouble concentrating in class, or show declining schoolwork. Teenagers sometimes downplay symptoms to avoid being pulled from sports — which makes it especially important for coaches and parents to recognize the signs independently and to follow “when in doubt, sit them out.”

Children’s brains are still developing, so proper evaluation and recovery are even more important. The American Academy of Pediatrics and CDC pediatric guidance recommend that any child suspected of having a concussion be evaluated by a healthcare provider and cleared before returning to sports or vigorous activity. Infants and very young children who hit their heads deserve a particularly cautious approach, because they cannot report symptoms and their signs are subtle.

When to See a Doctor vs. When to Go to the ER

Most concussions do not require an emergency room visit, but some do. Understanding the difference helps you act quickly when it counts while avoiding unnecessary visits when it does not.

See a doctor within a day or two if, after a head impact, you have a headache that is annoying but manageable, mild dizziness, difficulty concentrating, or sleep changes. Your primary care doctor, a sports medicine physician, or a neurologist can evaluate you and provide a management plan and return-to-activity guidance.

Go to the ER immediately for any of the red-flag symptoms in the box at the top of this article: loss of consciousness, a worsening or severe headache, repeated vomiting, seizure, slurred speech, weakness or numbness, unequal pupils, increasing confusion, unusual drowsiness or inability to wake, or clear fluid or blood from the nose or ears. These may indicate a brain bleed (intracranial hemorrhage) or skull fracture that requires imaging — typically a CT scan of the head — and possibly emergency treatment. Anyone taking a blood thinner (such as warfarin, apixaban, rivaroxaban, or dabigatran), taking daily aspirin, or living with a bleeding disorder should have a low threshold to be seen after any head injury, because bleeding risk is higher even when the initial injury seems minor. The same low threshold applies to adults over 65 and to infants and young children.

How Concussions Are Diagnosed

There is no single definitive test for concussion. Diagnosis is clinical, based on the mechanism of injury, the symptoms, and a neurological examination. Clinicians evaluate cognitive function (memory, concentration, orientation), balance, eye movements, and reaction time. Sideline and office tools from the 2023 Amsterdam consensus — the SCAT6 and Child SCAT6 for acute assessment, and the SCOAT6 for follow-up in the days after — provide a structured framework and have replaced the older SCAT5.

Imaging is not required for most concussions — a standard concussion does not show up on a CT scan or MRI, because the injury is functional rather than structural. CT scans are ordered when there is concern about a skull fracture, brain bleed, or other structural injury. Validated decision rules (such as the Canadian CT Head Rule for adults and PECARN criteria for children) help clinicians decide when imaging is warranted, sparing many patients unnecessary radiation while catching the injuries that matter.

Recovery Timeline and What to Expect

Most adults recover from a concussion within about two weeks, and most children and adolescents within about four weeks. A minority of people experience persistent symptoms lasting weeks to months — sometimes called persistent post-concussive symptoms — which often benefit from targeted rehabilitation (vestibular therapy, vision therapy, graded exercise, or help with mood and sleep) rather than continued rest.

Current guidance from the CDC and the 2023 Amsterdam consensus emphasizes a gradual, symptom-guided return. The outdated advice of “complete rest in a dark room until you feel normal” has been replaced by brief relative rest for 24 to 48 hours — reducing, not eliminating, physical and cognitive load — followed by a stepwise return to light activity as symptoms allow. Prolonged strict rest can actually slow recovery. Early, gentle, sub-symptom-threshold activity (such as a short walk) is now encouraged for many people, and light aerobic exercise that does not markedly worsen symptoms may help.

Return-to-learn and return-to-sport follow stepwise protocols. In each, the person advances one stage at a time, spends at least 24 hours at each stage, and drops back a step if symptoms clearly flare. Return-to-learn (school or work adjustments) generally comes before full return-to-sport. No athlete should return to contact sport the same day as a suspected concussion, and full contact should wait until a clinician has cleared them.

For symptom relief, ask your clinician what is appropriate for you. Acetaminophen is often suggested for headache, but you should check before using aspirin or NSAIDs (such as ibuprofen or naproxen) in the early period, particularly if a bleed has not been ruled out. This article does not provide medication doses; follow your clinician’s and the product label’s instructions. Avoid alcohol and recreational drugs while recovering, since they can worsen symptoms and mask warning signs.

Second-Impact Caution and Repeated Concussions

One reason clinicians insist on full recovery before return to play is second-impact syndrome — a rare but potentially catastrophic event in which a second head injury occurs before the brain has recovered from the first, leading to rapid, dangerous brain swelling. It is most feared in children, adolescents, and young adults. The practical rule is simple: when a concussion is suspected, the person comes out of the game or activity and does not go back until cleared.

Over the long term, repeated head trauma has been linked to chronic traumatic encephalopathy (CTE), a progressive brain condition identified in some athletes and military veterans; research on who is at risk and why is ongoing. While a single concussion typically resolves fully, repeated concussions — especially those occurring before recovery from a prior one — carry cumulative risk. This is why proper diagnosis, adequate recovery, and stepwise return protocols are not red tape but genuine safeguards.

Risk Factors for Concussion

Certain groups face higher concussion risk. Athletes in contact and collision sports — football, hockey, soccer, lacrosse, rugby — have among the highest incidence in young people. Female athletes appear to sustain concussions at higher rates than males in comparable sports (such as soccer and basketball), and some research suggests they may report longer recoveries, though the reasons are not fully understood.

Military personnel exposed to blast injuries are at elevated risk, as are older adults prone to falls. Young children are particularly vulnerable because of their proportionally larger heads, weaker neck muscles, and thinner skulls. People with a history of prior concussion, migraine, mood or anxiety disorders, or learning differences may take longer to recover and benefit from earlier, individualized care.

Blood thinners do not cause concussions, but they raise the risk of dangerous intracranial bleeding after head trauma — making any head impact more serious for people who take them. Patients on anticoagulants or antiplatelet drugs, and those with bleeding disorders, should seek emergency evaluation after head trauma even when they feel fine.

Frequently Asked Questions

Can you have a concussion without hitting your head?

Yes. A concussion can result from any force that causes the brain to move rapidly within the skull. Whiplash from a car crash, a blast wave, or a violent body impact can all cause a concussion without direct contact to the head. The mechanism is the rapid acceleration and deceleration of the brain, not the head impact by itself.

How long after hitting your head can concussion symptoms appear?

Some symptoms appear immediately, but others can develop 24 to 72 hours later. This is why monitoring for at least 48 hours after a head impact is wise. Any symptom that appears late or steadily worsens — especially a worsening headache, repeated vomiting, drowsiness, or confusion — is a reason to seek emergency care.

Should I wake someone up after a head injury?

For the first 24 hours after a suspected concussion, it is reasonable to check on the person periodically during sleep, briefly rousing them to confirm they are responsive and coherent. If they are hard to wake, confused when awakened, or show any red-flag symptom, seek emergency care. The old advice to “keep them awake all night” is outdated — sleep supports recovery — but brief check-ins are sensible, and any concern about waking them is an emergency.

When is it safe to return to sports after a concussion?

Return-to-sport follows a stepwise protocol in which the athlete must be able to complete daily activities and schoolwork without symptoms, then progress through light aerobic exercise, sport-specific exercise, non-contact drills, and finally full-contact practice — spending at least 24 hours at each stage and dropping back if symptoms flare. Medical clearance is required before full contact, and no athlete returns to play the same day as a suspected concussion.

Can repeated concussions cause long-term damage?

Repeated head trauma has been associated with chronic traumatic encephalopathy (CTE) and other long-term effects in some people, and research into the risks is ongoing. A single, properly managed concussion usually resolves fully. The cumulative risk from multiple concussions — particularly ones sustained before full recovery — is a major reason clinicians insist on adequate recovery time and return-to-play protocols.

What to Do Next

If you or someone you know has taken a hit to the head and is showing any of the signs described above, the most important step is evaluation by a healthcare provider. Do not “tough it out” or assume that no blackout means no concussion — most concussions occur without loss of consciousness. Watch closely for the red flags in the box at the top of this page, go to the ER for any of them, and otherwise see a clinician within a day or two for a proper diagnosis and a recovery plan. A clear plan — brief rest, then a gradual, symptom-guided return to learning and activity — is the fastest safe path back to feeling like yourself. If imaging is needed, our guide on CT scan costs explains what to expect financially, and our healthcare costs guide covers the bigger picture.

This article is for general education and is not medical advice. It does not include medication dosing. A head injury can be more serious than it first appears — when in doubt, seek in-person care, and call 911 for any emergency red flag.