Being concussed means your brain has been shaken or jolted inside your skull hard enough to temporarily change how it works. A concussion is a type of mild traumatic brain injury, but “mild” is a medical classification, not a description of how it feels. There’s no visible damage on standard brain scans. Instead, the injury disrupts your brain’s chemistry and electrical signaling, producing symptoms that can affect your thinking, mood, balance, and sleep for days to weeks.
What Happens Inside Your Brain
A concussion starts with a mechanical force: a blow to the head, a fall, or a sudden stop that causes the brain to shift and twist inside the skull. That movement stretches nerve fibers and disrupts cell membranes, setting off a chain reaction at the chemical level.
Within seconds of impact, brain cells release a flood of signaling chemicals and ions leak through damaged membranes. Potassium rushes out of cells while calcium floods in. Your brain’s recovery pumps kick into overdrive trying to restore balance, and those pumps burn through enormous amounts of energy in the form of glucose. The problem is that blood flow to the brain can drop to roughly half its normal level after injury. So at the exact moment your brain is demanding more fuel, it’s getting less. This mismatch creates what researchers call a cellular energy crisis.
After that initial burst of frantic activity, the brain shifts into a period of depressed metabolism. Excess calcium trapped inside cells impairs the tiny power generators (mitochondria) that produce energy, dragging out the crisis further. This is the biological reason why a concussed brain needs rest and time: it is literally running on a depleted battery while trying to repair itself.
How a Concussion Feels
Concussion symptoms fall into four broad categories, and most people experience some combination from each.
Physical symptoms are usually the most obvious. Headache is the most common, often accompanied by dizziness, balance problems, nausea (sometimes vomiting in the first hours), blurred vision, fatigue, and sensitivity to light or noise.
Thinking and memory problems can be subtle or dramatic. You might feel foggy, slowed down, or groggy. Concentrating takes extra effort, and short-term memory can be unreliable. Some people describe it as trying to think through mud.
Emotional changes catch many people off guard. Irritability, sadness, anxiety, and feeling more emotional than usual are all common. These aren’t personality changes. They’re direct effects of the brain’s disrupted chemistry.
Sleep disruption rounds out the picture. Some people sleep far more than usual, while others have trouble falling asleep or sleep less. Either pattern is typical after a concussion.
Not every concussion involves losing consciousness. In fact, most don’t. And symptoms don’t always appear immediately. Some develop over hours or even a day or two after the injury.
How Concussions Are Diagnosed
There is no single test that confirms a concussion. The diagnosis is a clinical judgment made by a healthcare professional based on what happened, what symptoms are present, and how the brain is performing on a series of checks.
In sports settings, professionals often use a standardized tool called the SCAT6 (Sport Concussion Assessment Tool), which takes at least 10 to 15 minutes to administer. It includes checks for observable warning signs like confusion, a blank stare, or balance problems. It also tests orientation (knowing the date, time, and place), short-term memory through word lists, concentration through tasks like reciting numbers backward, balance through standing on one leg and walking heel-to-toe, and coordination through finger-to-nose tests.
Even with all these components, a normal score on the SCAT6 doesn’t rule out a concussion. The tool is designed to support a diagnosis, not replace clinical judgment. Standard imaging like CT scans and MRIs typically appear normal after a concussion because the injury is chemical and electrical, not structural.
How Long Recovery Takes
Most children with a concussion feel better within two to four weeks. Adults generally recover in a similar window, though individual timelines vary widely. Several factors can stretch recovery longer: a history of previous concussions, more severe initial symptoms, pre-existing mental health conditions, learning difficulties, sleep problems, and high levels of stress at home or school.
Recovery isn’t purely passive. Modern management follows a graduated, step-by-step approach. The first priority is cognitive rest, meaning reduced mental demands like less screen time and lighter schoolwork. Once someone can handle a full day of school without symptoms, they move to light aerobic activity like riding a stationary bike. From there, they progress through running and sport-specific drills, then noncontact team drills, then full-contact practice, and finally return to competition. The key rule at every step: if symptoms return, you drop back to the previous stage and wait at least 24 symptom-free hours before trying again.
This step-by-step process exists because pushing through symptoms doesn’t speed healing. It can delay it. The brain needs to demonstrate it can handle each level of demand before taking on more.
Why a Second Hit Is Dangerous
The most serious risk during recovery is sustaining another head injury before the first concussion has fully healed. This is known as second impact syndrome, and while it’s rare, it can be catastrophic. A second blow to a still-recovering brain can cause the brain’s blood flow regulation to fail entirely. Pressure inside the skull rises rapidly, and the brain can herniate, meaning it gets pushed against the skull or through openings at the base of the skull. This can cause death within minutes.
Second impact syndrome is considered entirely preventable. The strategy is straightforward: don’t return to any activity that risks another head injury until you’ve fully recovered from the first one. This is the reason behind the strict return-to-play protocols used in youth and professional sports. No athlete should be cleared to compete while still experiencing any concussion symptoms.
Symptoms That Need Immediate Attention
Most concussions resolve on their own with appropriate rest and a gradual return to activity. But certain signs after a head injury suggest something more serious than a concussion, such as bleeding in or around the brain. Get emergency care if you notice a headache that keeps getting worse, repeated vomiting, seizures, increasing confusion, loss of consciousness lasting more than a brief moment, one pupil larger than the other, slurred speech, weakness or numbness in the limbs, or unusual drowsiness where the person can’t be woken. In young children who can’t describe their symptoms, watch for persistent crying that can’t be consoled and refusal to eat or nurse.