Concussion symptoms can linger for a while after the concussion has technically healed. There is no definitive answer to this question, as concussion symptoms can vary from person to person. However, in general, if a concussion sufferer feels like they are back to their normal self both physically and mentally, then they likely are concussion-free. If concussion symptoms persist after a reasonable amount of time (i.e. several weeks), it is advisable to speak with a doctor to rule out any other potential causes for the lingering symptoms.