Many people believe Post Tramatic Stress Disorder occurs when people have terrible experiences. PTSD actually occurs when people transition into a better situation. Once they transition into the better situation, they compare the past experience and start to get depress about it. The second thing with PTSD is that it is not a rational, conscious disease. Once the experience is over, association from sounds, sights that trigger the past event would cause the mind to recall the past event and put them in that depress state.
Because it is all about association and emotions, it has nothing to do with rational thought. It serves no purpose. The mind is just protecting itself from future occurrences. The solution is then to disassociate from the triggers. There are many books on how you can remove irrational associations. Even just being aware it, you can tell yourself this is just an irrational, unimportant reaction from the mind and no longer serves any purpose, so you can make a conscious effort to remove the association/triggers.