During a concussion, the brain slides back and forth against the inner walls of the skull. This forceful movement can be caused by a violent blow to the head and neck or upper body. It also may be caused by the sudden acceleration or deceleration of the head. This may happen during a car crash, a fall from a bike or from a collision with another player in sports. These movements injure the brain and affect brain function, usually for a brief period of time. Sometimes a mild traumatic brain injury can lead to bleeding in or around the brain, causing prolonged drowsiness, confusion and, sometimes, death. Anyone who experiences a brain injury needs to be monitored in the hours afterward and seek emergency care if symptoms worsen.