However, your feedback is important to us. Post-concussion syndrome, or post-concussive syndrome (PCS), refers to the lingering symptoms following a concussion or a mild traumatic brain injury (TBI). It is typically diagnosed when a person who has recently suffered a head injury continues to feel at least three of the main symptoms following a concussion. These include dizziness, fatigue, and headaches. Post-concussion syndrome can begin to occur within days of the head injury.