We need to understand that trauma to the head is relative.

<But for a PCS brain, a mild bump to the head that presumably wouldn't cause any considerable physical damage, may result in a return or worsening of symptoms due to the brain's sensitivity.>

If the trauma is intense enough to cause damage to a very sensitive brain, this relative rate of intensity to sensitivity can be considered a concussion or even a sub-concussive impact. The issue of 'considerable physical damage' is the important point.

<Does this indicate significant new damage, or more that a very small amount of damage added to the original damage that caused the PCS in the first place results in a worsening of symptoms.>

"More than a very small amount of damage" is a relative term. If there is damage, whether intense or very small in nature, this is still damage. It may only cause a chemical reaction. But, that chemical reaction may cause the physical damage.

The brain reacts to insults with a cascade of events. These may include a 'self destruct' instruction to the damaged cells and those nearby that have been stressed.

The decompensation event is usually a result of non-impact stresses. Excessive mental effort, mental fatigue, mental shock as in a adrenaline reaction to a high intensity event, high fever, chemical insult as in alcohol, drugs, food toxins or environmental toxins, etc. can stress the brain from a neuro-chemical direction.

Eddy, subsequent concussions lead to Multiple Impact Syndrome. Each successive concussion of the same intensity does more damage by increasing factors. For example, if your first concussion was an impact energy level of 5 (a random value) and caused damage at a level of 5, a successive concussion of impact energy level of 5 could easily cause damage at a level of 10. A third impact of level 5 could result in damage at a level of 20. Or, a third impact of level 2 could result in damage at a level of 10.

There is no medical/scientific formula for this increasing progression of damage. It is just know that each successive impact causes more damage. The brain ability to recover declines as the number of concussions increases. There comes a point where the brain is struggling with damage to a point that it is less able to heal or recover because it is using all of its capabilities to just endure the injury.

Think of trying to move into a strong wind. At first, one can move into the wind. As the wind increases or continues, the body tires and forward movement become more difficult. At time may come where forward progress is no longer possible. At this point, any increase in wind strength will actually push the person back.

I have Multiple Impact syndrome. I have had 13 concussions over 45 years. I can now get a concussion shaking my head 'NO.' There are others on this forum with the same sensitive brains. Some have tried to say that these head shake moments are not concussions.

My most common concussion symptom is a taste of metal, like I am chewing aluminum foil. I also get a feeling like I got punched in the nose. I may feel dizzy but more likely feel foggy in my thinking. I may feel nauseous.

A decompensation will not have these symptoms. I will just feel mentally tired and easily overwhelmed with sensory input (sound and visual). I can decomp from being in an intense discussion with a single person, or in a room full of people talking.

I can be in a group of people and finally need to walk away and find a quieter spot. My mind goes sort of blank and I retreat to a safe place.

I have had times when it took up to two weeks to recover from a decompensation. This happened after my Work Comp hearing with the administrative law judge.

The important point is to learn how to recognize these different events, discover the trigger, whether it was a head shake or too much stimulation, and develop behavioral habits to avoid them in the future. It is believed by some researchers and physicians that even decompensations are cumulative in nature. At best, they can delay recovery. At worst, they can cause worsening of symptoms.

There is an old saying; Live and learn. The PCS person has to endeavor to do both.