I have been doing a lot of reading as well as listening to therapists I have had explain it to me. They are studying the brain constantly to figure out what is happening in the brain of someone suffering from PTSD as we are losing so many vets that come home crippled with it. I have been reading about it constantly for the past 10 years as it has crippled me and I could not understand it or even how to reduce the often "intrusive" symptoms it presents. Some people have it worse than others so a lot depends on the person and the trauma they experienced along with how sensitive that person is.