dr. mardi horowitz is a psychiatrist at the university of california medical school at san francisco and an authority on post-traumatic stress disorder. post-traumatic stress disorder has three important elements-- one is that there has been a trauma, experience that's usually extraordinary for the person and shocking very frequently, often terrifying or having a death anxiety or a big terror event involved. and the second component is often some kind of intrusive experience, whether it's of a pang of very intense emotion, a recurrent visual image repeating the perceptions. and the third component is often a kind of numbing or denial or omitting of memories that one would expect after such a serious life event. man-made disasters tend to create more victims of post-traumatic stress disorder than do natural ones. so it was that many veterans of the vietnam war showed signs of ptsd after returning. almost 16 months of my life was spent in a jungle. i'd seen a base camp only two months, and that was a wk here and a week there. the rest was living with bugs. now bugs bother me. loud noises--