rydellen has it right. My neurologist, after seeing my brain functions on a qEEG, AEP and VEP and understanding my past history of concussions and partial recovery, believes that I had finally hit that point of damaging the critical mass of brain cells needed to continue full function.

In the past, I would have symptoms of cognitive struggles that would recover except for times of stress. Now, my brain performs like it did just after the previous concussions or during previous times of stress

My brain is now 24/7 in a state of dysfunction with even worse dysfunction during times of stress/overload.

One of the things that may be a part of the delayed symptoms is the brains tendency to share work load. If function A has lost 50 % of its functional ability, can it draw from an area of the brain that supports function B? If function B was at 90 % functional capacity, it may drop to a 70% functional level to allow function A to utilize some of the functional capacity and recover to ... maybe 65% functional capacity.

This happens when a function is not longer needed. When someone goes blind or has their eyesight temporarily blocked, the brain cells that support eye sight can be used by other sensory systems. The might allow hearing to become very acute by using unused vision processing cells to increase the auditory processing function. The fMRI studies and such have shown this sharing of brain cells can take place rather quickly, within 12 to 24 hours or less.

It would appear to make sense that the brain would share good cells with areas that lost cells to concussion damage. This sorting out of brain cell function could easily be part of the delayed symptoms. It could explain why some concussion subjects appear to, over time, recover in some functions but degrade in other functions. An intense imaging study of this would be very interesting.