There is definitely a connection between brain chemistry at the time of impact and the PCS intensity. The brain under stress does not properly metabolize and excrete the results of metabolism. There is also adrenaline and other chemical processes that go on at higher levels. the byproducts of the stress related functions do not get completely purged from the brain. As a result, the brain is in a weakened state and less able to tolerate and recover from impacts. Depression is a symptom of this chemical pollution. PTSD is similar except it causes physiological changes too.

Now comes an impact. The brain is polluted with these various chemicals. It is like having the flu and hay-fever allergies at the same time. Both conditions are magnified because of the weakened immune state. The brain is just the same. It needs to go through a healing process but is still overwhelmed with the stress toxins. Not only does the healing not happen, either right away or completely, but the weakened brain cells are more prone to damage.

This was explained to me in 1982 when I had a very bad reaction to a stressful event.

This is why mTBI and PCS persons need to be diligent in their nutrition and stay away from toxins such as alcohol, exitotoxins, and stress.