Most concussions resolve on their own within days to weeks, but certain warning signs signal something far more dangerous, like bleeding or swelling inside the skull. Knowing the difference between typical concussion symptoms and true emergency signs can be lifesaving. The key is watching for symptoms that get worse over time rather than gradually improving.
Emergency Warning Signs in Adults
A concussion crosses into dangerous territory when pressure builds inside the skull, usually from a blood clot or swelling compressing the brain. These are the signs that mean you or someone nearby should call 911 immediately:
- A headache that keeps getting worse and won’t respond to rest or over-the-counter pain relief
- Repeated vomiting, not just once from the shock of the injury
- Seizures or convulsions, any shaking or twitching
- One pupil larger than the other, which can indicate dangerous pressure on one side of the brain
- Slurred speech or worsening confusion
- Weakness, numbness, or loss of coordination on one side of the body
- Increasing drowsiness or inability to stay awake
- Loss of consciousness
- Not recognizing familiar people or places
The pattern matters more than any single symptom. A mild headache after a bump to the head is expected. A headache that steadily intensifies over the next few hours is not. Feeling groggy is common after a concussion. Being unable to wake someone up is an emergency.
Why Symptoms Can Appear Hours or Days Later
One of the most dangerous aspects of head injuries is the “lucid interval,” a period right after the impact where someone feels relatively fine before symptoms suddenly worsen. This happens because bleeding inside the skull can be slow. A small blood vessel tears on impact, blood gradually pools, and pressure on the brain builds over hours or even weeks.
There are different types of bleeding that behave differently. Some cause immediate drowsiness or loss of consciousness from the moment of injury. Others, particularly bleeding between the skull and the brain’s outer covering, can take days or weeks to produce noticeable symptoms. This is why someone who “seemed fine” after a head injury can deteriorate later. The subacute type is especially tricky because by the time symptoms appear, the person may not even connect them to the original injury.
Because of this delay, anyone who has taken a significant blow to the head should be monitored closely for at least 24 to 48 hours. If you’re checking on someone, wake them periodically during sleep for the first night and watch for any of the emergency signs listed above.
How Doctors Decide If You Need a CT Scan
Not every concussion requires brain imaging. Emergency physicians use a well-validated set of criteria to decide who needs a CT scan. Five factors indicate high risk for a serious injury requiring intervention: not returning to full alertness within two hours, signs of a skull fracture, vomiting two or more times, and being 65 or older. Two additional factors raise moderate concern: memory loss extending more than 30 minutes before the impact, and a dangerous mechanism of injury (like being hit by a car or falling from a significant height).
If none of these apply, your odds of having a serious brain injury are very low, and a CT scan likely won’t show anything. But if even one high-risk factor is present, imaging is strongly warranted. This is useful context if you’re sitting in an ER wondering whether the doctor is taking your injury seriously enough, or if you’re debating whether to go in the first place.
Unequal Pupils: Why This Sign Is So Urgent
One pupil being noticeably larger than the other after a head injury is one of the most critical warning signs. It suggests that rising pressure inside the skull is compressing the nerve that controls pupil size. This is the same mechanism seen in strokes and brain aneurysms, and it can indicate the brain is being pushed out of its normal position. If you notice this in someone who has hit their head, treat it as an emergency even if they seem otherwise alert.
The Risk of a Second Impact Too Soon
Returning to physical activity before a concussion has fully healed creates the risk of a rare but catastrophic condition. If the brain takes a second hit while still recovering from the first, it can lose the ability to regulate its own blood flow. The result is rapid, severe brain swelling that is often fatal or causes permanent disability. Most documented cases have involved adolescents and young adults in contact sports like football, hockey, and boxing.
This is why return-to-play protocols exist in youth and professional sports, and why “pushing through” concussion symptoms is genuinely dangerous, not just cautious advice. Full cognitive and physical recovery from the first concussion needs to happen before any risk of re-injury.
Warning Signs in Babies and Young Children
Children under four can’t tell you they have a headache or that their vision is blurry, so you have to read behavioral cues. After a bump to the head, watch for crying that won’t stop and can’t be soothed, refusal to eat or nurse, changes in sleep patterns, appearing dazed or unusually clumsy, and speaking more slowly than normal. Vomiting right after the injury (without another explanation like a stomach bug) is also a red flag.
The emergency signs are the same as for adults: seizures, inability to recognize caregivers, repeated vomiting, one pupil larger than the other, increasing drowsiness, and loss of consciousness. In an infant or toddler, inconsolable crying and complete refusal to eat are treated with the same urgency as these danger signs because they may be the only way a very young child can express severe pain or neurological distress.
When Symptoms Linger for Months
Some people develop persistent symptoms that last well beyond the normal recovery window. Headaches, dizziness, difficulty concentrating, irritability, and sleep problems that continue longer than three months after the injury fall into a category called persistent post-concussive symptoms. These typically begin within the first 7 to 10 days and, while they usually resolve within a few months, they can sometimes last a year or more.
Lingering symptoms don’t necessarily mean there’s bleeding or structural damage in the brain. They reflect ongoing disruption in how the brain processes information, regulates mood, and manages sensory input. But prolonged symptoms do warrant medical evaluation, both to rule out other causes and to get access to treatments like vestibular therapy, cognitive rehabilitation, or carefully guided return to exercise, all of which can speed recovery significantly compared to simply waiting it out.
What “Mild” Actually Means
Concussions are classified as mild traumatic brain injuries, which can feel misleading when you’re struggling with headaches and brain fog. The “mild” label comes from a clinical scoring system that rates eye opening, verbal responses, and physical movement on a scale of 3 to 15. A score of 13 to 15 is classified as mild (concussion), 9 to 12 as moderate, and 3 to 8 as severe. So “mild” doesn’t mean trivial. It means the brain injury didn’t cause prolonged unconsciousness or major neurological deficits at the time of evaluation. You can still feel terrible and take weeks to recover from a “mild” injury.
The practical takeaway: a concussion is serious when symptoms escalate rather than plateau or improve. Worsening headache, increasing confusion, new vomiting, or any loss of consciousness in the hours and days after a head injury all point to something beyond a routine concussion, and all warrant immediate emergency evaluation.