Dr. Sharon Lambert:

Some people, and we all know such people, have a very wide window of tolerance where no matter what is going on and no matter what the stressor is, they have a plan B, C, D and E and they can think really straight. Other people have what we call a very narrow window of tolerance, so when there is a stressor they leave their window of tolerance. When we leave our window of tolerance we can become hyper-aroused, that is, angry, irrational and irritated, or we can become hypo-aroused. The latter are the people who become very withdrawn. What is really interesting is that when we talk about trauma - we know all the signs of trauma and stress and how they impact on a body - two people could experience the same trauma but one of those people can become hyper-aroused, so very irritated, and the other can become hypo-aroused, so very withdrawn. Those in one of those groups are very easy to deal with because they just withdraw and disappear but you have exactly the same thing going on except their ability to manage stress is gone.