So people think you like to think that you are "super-human". Everything in you has been trained to expand beyond the average capacity. But, at the end of the day, you are just as fragile as the average person.

Everyday you witness traumatic situations. And, no matter how long you have worked as a Police Officer or Emergency Worker, you never become immune to the tragedies and human suffering you witness.
As time goes on, you either learn to live with it or to cope with these scenes better or you head rapidly towards breaking point.
You can call it burn out, a breakdown, cracking or whatever you want, the fact remains that no matter how hard you try to deny it, you experience a very high level of emotional stress.
And if you do not dealt with, at it's best result in suicide (many studies show that factors which pre-dispose a person to suicide include exposure to a traumatic situation/s as well as being exposed to suicide/suicidal behaviour in others).

I am not an expert of Post Traumatic Stress, however I do believe very strongly that the threat of this disorder is always present in Police and Emergency personnel. It is a threat which is often ignored or brushed off. In some stations it is even taboo to consider that a Police Officer or Emergency Worker may be emotionally traumatised by their work.

We are talking about a situation where you exprience or witnesses or is confronted with an event that involves actual or threatened death, serious injury or even a threat to physical integrity of one's self or others. This includes an event outside the usual range of experiences which is so powerful and sudden that it can overwhelm your ability to cope (either at the scene itself or later on).
Examples even include dealing with death, violence, destruction of property, personal danger and acute discomfort.

Even though you seldom witness the actual accident or violent act which has occured, you witness the result. This does not only include the physical trauma from which a person is suffering, it can include having to listen to someone begging you not to let him die, which is especially traumatic if your efforts are unsuccessful! Or someone begging you not to respond because they are scared your reaction will make the pain or situation worse, bringing on a feeling of helplessness as you know that in order to give them a chance on living, you must react but also knowing you are inflicting pain or fear on them.
I also know of personnel who have experienced extreme trauma after having to treat or respond to a family member or friend. Like the man who had to resus his drowned son! Fortunatley the resus was completely successful.
It seems that incidents involving children have a specific emotional impact on those treating them.
Multiple scenes can also be traumatic, especially if you are first to arrive on scene.
These are just a few expamples of incidents. I am sure you can relate well to them. There are obviously many more which you can call on from your own experience.