I have posted about how the brain can memorize a reaction to a situation like a light head bump as being the same as a concussion. Here is a better explanation with the technical details.

I found this in the comments on a question about aircraft flying through turbulence on quora.com. It sounds like it is the medical/psychological explanation for why so many experience so many symptoms from just a head bump after they suffered a concussion.

"Why are people so afraid of turbulence during an airline flight? It is because the amygdala, the part of the brain that releases stress hormones reacts every time it feels a dropping sensation. This means every time the plane drops in turbulence, every passenger gets another shot of stress hormones.

Everyone gets the stress hormones (other than the pilots whose amygdala is desensitized to turbulence). People who automatically regulate arousal caused by stress hormones, self-regulate. People who do not automatically regulate arousal caused by stress hormones, get more, and more revved up with “fight or flight” response feelings. And, with no control, and unable to fight or flee, the stress hormones build up, and cause panic.

Then, in the amygdala itself, there are memory cells which record the release of stress hormones and the fear and panic. This is a form of PTSD. The person, having been terrified by turbulence, simply believes it is dangerous based on what is recorded in the amygdala. They cannot change what they believe because the memory cells involved with this in the amygdala are fixed.

Based on my experience treating fearful fliers, nothing can be done to fix this other than to train the mind to produce oxytocin during the flight. Oxytocin inhibits the amygdala. Some people say they want to be knocked out when they fly. That isn’t necessary. Why? Because we can just knock out the amygdala by producing oxytocin."

Quora - The best answer to any question

To apply this to PCS. The concussion creates a memorize sensitivity in the amygdala to head movement. This is connected to the memory of concussion symptoms. So, when the head experiences a sudden movement, it reverts to concussion symptom mode.

This is why I tell people to practice desensitizing their brain to touch by touching and tapping on their head or having somebody else do it when it is not expected. This is an attempt to retrain the brain to a new, less stressful response pattern.