A concussion is a brain injury caused by a bump, blow, or jolt to the head (or body) that makes the brain move rapidly inside the skull. It’s not a bruise on the brain or a structural wound that shows up on a standard CT scan. Instead, it’s a disruption in how brain cells function, triggered by the physical forces of impact. Most people recover within two to four weeks, but the injury requires careful management to heal properly.
What Happens Inside the Brain
Your brain floats in cerebrospinal fluid inside your skull. When your head accelerates and then suddenly stops, or rotates quickly, the brain shifts and twists against the skull’s interior. Rotational acceleration plays a particularly important role in the injury. This movement stretches and strains the long fibers (axons) that connect brain cells to each other, disrupting their normal communication.
At the cellular level, that mechanical strain sets off a chain reaction. Damaged cells release a flood of a chemical messenger called glutamate, which forces open channels in nearby cell membranes. Potassium rushes out of the cells while sodium and calcium rush in. This ionic imbalance essentially short-circuits normal brain signaling. The brain then has to burn through enormous amounts of energy to restore balance, at a time when its blood flow and energy supply may already be compromised. That mismatch between energy demand and energy supply is a major reason concussion symptoms can linger.
Recognizing the Symptoms
Concussion symptoms fall into four broad categories: physical, cognitive, emotional, and sleep-related. They don’t always appear immediately. Some develop hours or even days after the injury.
Physical symptoms are the most recognizable. Headache is the most common, often accompanied by nausea, dizziness, blurry vision, ringing in the ears, fatigue, sensitivity to light and noise, and sometimes slurred speech. Loss of consciousness happens in only a minority of concussions, so being “knocked out” is not required for the injury to be serious.
Cognitive symptoms include feeling foggy or confused, difficulty concentrating, slowed responses to questions, memory problems, and amnesia surrounding the event itself. People sometimes repeat the same question without realizing they already asked it.
Emotional and sleep symptoms are often overlooked but equally real. Irritability, feeling unusually emotional or depressed, and personality changes can all follow a concussion. Sleep disruptions, whether sleeping too much or too little, are common as well.
How a Concussion Is Diagnosed
There is no single blood test or brain scan that confirms a concussion. Standard imaging like CT scans and MRIs are typically normal because the injury is functional, not structural. These scans are sometimes ordered anyway to rule out more dangerous injuries like bleeding in or around the brain.
Instead, diagnosis relies on clinical evaluation. A healthcare provider will assess your symptoms, test your balance, check your eye movements and vestibular function (how your inner ear and brain coordinate balance and spatial awareness), and evaluate your memory and concentration. In sports settings, clinicians use a standardized assessment called the SCAT6, which combines symptom checklists, cognitive tests, and balance evaluations into a single tool. An office-based version adds specific tests for balance errors and visual-motor function.
Recovery: Rest, Then Gradual Activity
The old advice was to lie in a dark room for days or weeks. That’s changed significantly. Current guidelines from the American College of Sports Medicine recommend a brief period of relative rest, roughly 24 to 48 hours, during which you can do light daily activities like walking as long as they don’t make symptoms worse. After that initial window, early aerobic activity such as walking or stationary cycling is encouraged, as long as it causes no new symptoms or only mild ones that resolve within an hour.
Most children with a concussion feel better within two to four weeks. Adults generally follow a similar timeline, though individual recovery varies based on factors like concussion history, age, and the severity of the initial symptoms.
Returning to Sports and Activity
For athletes, the CDC outlines a six-step return-to-play progression, with each step requiring a minimum of 24 hours before advancing to the next. If symptoms return at any step, you drop back to the previous one.
- Step 1: Return to regular daily activities like school or work, with clearance from a healthcare provider.
- Step 2: Light aerobic activity only, such as 5 to 10 minutes on a stationary bike or light jogging. No weight lifting.
- Step 3: Moderate activity that increases heart rate with body or head movement, including moderate jogging and reduced-intensity weight lifting.
- Step 4: Heavy non-contact activity like sprinting, full weight lifting routines, and sport-specific drills.
- Step 5: Full practice including contact, in a controlled setting.
- Step 6: Return to competition.
This progression exists for a critical reason. Returning to contact activity too early, while the brain is still recovering, creates the risk of a far more serious injury.
Second Impact Syndrome
When someone sustains a second head injury before their first concussion has fully resolved, they can develop second impact syndrome. Within seconds to minutes of the second hit, the person may experience rapidly altered mental status and sometimes loss of consciousness. The brain swells catastrophically, and the condition carries a high rate of permanent disability and death. Notably, all documented cases with poor outcomes (death or permanent disability) occurred in individuals younger than 20 years old. This is the primary reason young athletes are held out of play until fully recovered and cleared.
Danger Signs That Require Emergency Care
Most concussions resolve on their own with proper management, but certain symptoms after a head injury signal something more serious, like bleeding in or around the brain. Call 911 or go to an emergency department if you notice any of the following:
- Seizures or convulsions
- A headache that keeps getting worse and won’t go away
- Repeated vomiting
- Increasing confusion, restlessness, or agitation
- Inability to wake up or stay awake
- Slurred speech, weakness, numbness, or loss of coordination
- One pupil larger than the other, or double vision
- Inability to recognize familiar people or places
In infants and toddlers, look for the same signs along with inconsolable crying and refusal to eat or nurse. Young children can’t describe symptoms like fogginess or headache, so behavioral changes are often the clearest indicator that something is wrong.