A somewhat technical explanation is this. The brain has a function that everybody else takes for granted. It is a filtering mechanism that helps the brain ignore most of the stimulation in our environment. Think of it as sunglasses for light, sound, visual images, tactile sensations, even smells.

The injured brain may be able to filter out these excess stimuli for a while but as the brain fatigues from this same over-stimulation, this system can suddenly stop completely.

For those 'friends' willing to watch it, there is a good video series on YouTube called "You Look Great." The first segment of 6 is at http://www.youtube.com/watch?v=x9Xso...ature=youtu.be . It takes about an hour to watch all 6 segments.