As I mentioned in another post, PTSD is like having all your memory files dumped on the floor of your brain! The stress chemicals at the time of trauma is the cause. Therapy, And the skills you learn will begin to retrain the brain in how to file them again and correctly. The good news is that once you process a memory, the brain will go on and file all similar memories as well.. So you will not have to go through each and every memory.