Quick answer
The CDC states that “some mild TBI and concussion symptoms may appear right away, while others may not appear for hours or days after the injury.”[1] Its HEADS UP program adds that signs and symptoms “may take hours or days to appear or be noticed,” and that symptoms are usually most severe 1 to 2 days after the injury.[2] When symptoms appear later, a first medical record may not mention them.
What the CDC says
The CDC groups mild TBI symptoms into four categories:[1]
Physical
Headaches, dizziness or balance problems, nausea or vomiting early on, feeling tired, vision problems, and being bothered by light or noise.
Thinking and remembering
Attention or concentration problems, feeling slowed down, feeling foggy or groggy, memory problems and trouble thinking clearly.
Social or emotional
Anxiety or nervousness, irritability, feeling more emotional and sadness.
Sleep
Sleeping less or more than usual and trouble falling asleep.
HEADS UP notes that symptoms “may change during recovery.”[2]
Why symptoms may be noticed late
After a crash or fall, more obvious injuries and the stress of the event can draw attention away from subtle cognitive symptoms. Some symptoms, such as trouble concentrating at work or school, may only become apparent when the person returns to normal demands. HEADS UP describes signs as taking time “to appear or be noticed,”[2] which includes being noticed by others.
Delayed symptoms and medical records
An emergency department record made shortly after the injury may focus on the most urgent findings. If a headache, memory problem or dizziness appears later, the first record that mentions it may be days or weeks after the injury. A gap like that can be used to argue the symptom is unrelated. Follow-up records that explain when symptoms started, and how they relate to the injury, address that argument directly.
Documenting the timeline
A written record kept close in time, such as a symptom journal, messages to family or notes from an employer, can corroborate when symptoms began. See everyday evidence. Patients can also request their records to check that symptoms they reported were recorded. See medical records.
Delayed symptoms and legal deadlines
Statutes of limitations may run from the date of injury or, in some cases, from the date an injury was discovered or should have been discovered.[3] Claims against governments can have much shorter notice periods.[4] See claims against the government.
Frequently asked questions
How long after a head injury can symptoms start?
The CDC says some symptoms may not appear for hours or days after the injury.[1]
When are concussion symptoms usually worst?
HEADS UP says symptoms are usually most severe 1 to 2 days after the injury.[2]
This page provides general information from the sources listed below. It is not legal or medical advice, and reading it does not create an attorney-client or provider-patient relationship. Laws vary by state and change over time. See our legal disclaimer.
Sources
- Centers for Disease Control and Prevention. “Symptoms of Mild TBI and Concussion.” https://www.cdc.gov/traumatic-brain-injury/signs-symptoms/index.html
- Centers for Disease Control and Prevention, HEADS UP. “Signs and Symptoms.” https://www.cdc.gov/heads-up/signs-symptoms/index.html
- Legal Information Institute, Wex. “Statute of limitations.” https://www.law.cornell.edu/wex/statute_of_limitations
- 28 U.S.C. § 2401, Time for commencing action against United States. Legal Information Institute. https://www.law.cornell.edu/uscode/text/28/2401
Sources last checked: October 11, 2026
