The surprise or startle or shock from bumping one's head is not a concussion symptom. It is anxiety. It is no different than most other startles like having to make an emergency stop or evasive turn in the car to avoid an accident. It is a learned response. Before being concussed or sensitized to concussions from watching somebody else get a concussion, you would not have reacted to the bump with anything more than annoyance.

Soldiers who have returned from combat where loud pops were a threat often react to loud sounds as if they are threatening gun shots or explosions. The loud sound could be a car back firing or something being dropped or fireworks. It is not threat at all but the response by the veteran can be as if it is. This is a learned response. In some cases, it is magnified by PTSD.

Researchers and concussion trained doctors know that people who already have a tendency to have anxiety responses will react to non-injury bumps as if they were serious concussions.