Symptoms. When a person receives a concussion, they will initially see a flash of light. Some may describe this as “seeing stars.” They usually won’t become unconscious though. Within a few minutes, confusion and fatigue will set in. Then, an intense headache will develop. Vomiting and nausea are also common, but only for the first few hours. The other symptoms will last for about six months in adults unless they have had prior concussions, which can extend the healing time by a few more months.