The hallmark symptom of a concussion is a persistent headache, as it reflects ongoing brain irritation and trauma at the cellular level. While loss of consciousness can occur, it is not present in most concussion cases. Seizures and vomiting are less common and suggest more severe brain injury or complications. Recognition of persistent headache is crucial for timely diagnosis and management to prevent further brain damage. This symptom guides clinicians in assessing the severity and monitoring recovery.

Reference: Adams and Victor’s Principles of Neurology, 11th Edition.