A concussion causes a recognizable pattern of symptoms after a bump, blow, or jolt to the head. The most common signs are headache, dizziness, confusion, and nausea, but not everyone gets all of them, and some symptoms can take hours or even days to show up. You don’t need to lose consciousness to have a concussion. In fact, most people with concussions never black out.
Physical Symptoms That Appear First
Headache is the single most common concussion symptom. It often starts within minutes of the injury, though it can also develop gradually over the next few hours. Along with the headache, you may notice dizziness or trouble keeping your balance, nausea or vomiting, blurred or double vision, ringing in your ears, and sensitivity to light or noise. You might also feel profoundly tired, as if your energy has been drained all at once.
Nausea and vomiting tend to happen early, usually in the first hour or two. If the vomiting continues or gets worse rather than settling down, that’s a red flag that needs emergency attention (more on that below).
Cognitive and Emotional Changes
A concussion disrupts normal brain function, so the symptoms aren’t only physical. You may feel confused or “foggy,” have trouble concentrating, or struggle to remember what happened right before or after the impact. Some people describe it as feeling mentally slowed down. Repeating the same question without realizing it is a classic sign that others around you may notice before you do.
Emotional shifts are common too. Irritability, sadness, anxiety, or mood swings can appear in the hours and days after a head injury. These aren’t signs of a separate problem; they’re part of the concussion itself. Sleep disruption rounds out the picture. You might have trouble falling asleep, sleep more than usual, or feel drowsy during the day.
Symptoms That Show Up Later
Not every concussion symptom appears right away. Some develop hours or days after the injury, which catches a lot of people off guard. Difficulty concentrating, memory problems, personality changes, sensitivity to light and noise, and sleep issues are the symptoms most likely to be delayed. This is why it’s important to monitor yourself (or have someone else keep an eye on you) for at least 24 to 48 hours after a head impact, even if you feel fine initially.
A person can walk away from a collision, pass a quick sideline check, and still develop clear concussion symptoms the next morning. Delayed onset doesn’t mean the injury is less serious.
What Someone Else Might Notice
Concussions can be hard to self-diagnose because they affect the very organ you’d use to assess yourself. People around you may pick up on signs before you do: a dazed or vacant look, slurred speech, clumsiness or coordination problems, confusion about where you are or what’s happening, or asking the same question over and over. If anyone around you mentions that you seem “off” after a head impact, take that seriously.
Signs in Infants and Toddlers
Young children can’t tell you their head hurts or that things look blurry. In infants and toddlers, watch for inconsolable crying, refusal to nurse or eat, changes in sleep patterns, loss of interest in favorite toys, unsteadiness when walking or crawling, and a generally irritable or listless demeanor. Any of the emergency danger signs listed below also apply to young children.
Danger Signs That Need Emergency Care
Most concussions resolve on their own, but some head injuries are more severe than they first appear. Call 911 or go to an emergency department if you notice any of the following after a head impact:
- A headache that keeps getting worse and won’t go away
- Repeated vomiting
- Seizures or convulsions
- One pupil noticeably larger than the other
- Increasing confusion, restlessness, or agitation
- Inability to wake up or stay awake
- Slurred speech, weakness, numbness, or loss of coordination
- Not recognizing familiar people or places
These signs can indicate bleeding or swelling inside the skull, which is a medical emergency.
How Concussions Are Diagnosed
There’s no single blood test or brain scan that confirms a concussion. Diagnosis is a clinical judgment, meaning a healthcare provider evaluates your symptoms, mental function, balance, coordination, and eye movements to determine whether you have one. Clinicians often use a standardized assessment that includes memory questions, balance tests, and a symptom checklist covering 22 different symptoms scored by severity.
Brain imaging like a CT scan is not typically needed for a straightforward concussion, and a concussion will usually look normal on a CT or MRI. The purpose of imaging is to rule out something worse, like a skull fracture or bleeding in the brain. A CT scan is generally recommended if you’ve vomited two or more times, lost consciousness, can’t remember the 30 minutes before the injury, were hit by a car or fell from a significant height, or are over 65. If the scan comes back normal, that doesn’t mean you’re fine. It means you don’t have a structural injury, but you can still absolutely have a concussion.
What Recovery Looks Like
Most concussion symptoms resolve within two to six weeks. During that time, the most important thing is to give your brain a chance to heal. This doesn’t mean lying in a dark room for days (that outdated advice has been replaced), but it does mean avoiding activities that make your symptoms significantly worse.
If you’re an athlete, returning to sports follows a six-step progression. You start with light aerobic activity like walking or slow biking for 5 to 10 minutes. If that doesn’t trigger symptoms, you move to moderate activity the next day, then heavier non-contact exercise, then full practice with contact, and finally competition. Each step takes a minimum of 24 hours. If symptoms return at any step, you drop back to the previous level and rest before trying again. The same principle applies to returning to work or school: gradually increase your mental and physical load, and back off if symptoms flare.
When Symptoms Linger
About 15% of people with a concussion develop post-concussion syndrome, where symptoms persist for months or even longer than a year. The most common lingering symptoms are headaches, difficulty concentrating, fatigue, dizziness, and mood changes. A diagnosis of post-concussion syndrome is typically considered when symptoms last beyond three months. If your symptoms aren’t improving within a few weeks, or they’re getting worse instead of better, that’s worth a medical evaluation to explore targeted treatment options like vestibular therapy, vision therapy, or guided exercise programs.