A lot of people who experience trauma and then find themselves jumping at sounds, panicking at a bonfire or even dropping into isolation and depression, ask 'what is wrong with me?' The honest answer... absolutely nothing. These reactions will occur when the body interprets an event to be threatening, or thought to be harmful.
The body is designed to either "flight, freeze or fight" when it senses it is in danger. That is why some people when asked why they did not run will shamefully reply that they couldn't. It is the truth, if the flight mechanism is freeze, they cannot move.
I experienced this with a cougar once. My brain was screaming to go back in the house but I couldn't move a muscle. I was frozen. I couldn't understand why my body would not respond to the thought "I WANT TO LEAVE."
The body will respond to the thought 'I am danger.' It doesn't matter how the event occurred. It doesn't matter if it is a loss of job, robbery, house fire or natural disaster. There are some traumas that wound on a much deeper level. These are often harmful childhood events or violence from someone we love or have loved.
The problem arises when the body becomes hyper-vigilant. Much like a deer being hunted, we will look around wildly and the body becomes ready for one of the danger responses when something is perceived as potentially dangerous. You can see this in action when some returning soldiers goes to a 4th of July celebration and then drops to the ground at the first explosion. His body has trained for this trigger and will fall back to it even when there is no threat.
See, we have two types of brain. A new brain and an old brain. The old brain holds the responses to danger. The new brain analyzes if there is really danger. The old brain gets signals faster than the new brain can process. So the thought 'I am at fireworks' doesn't occur till the soldier is already on the ground.
This is why many coaches and definitely counselors teach grounding techniques to give the new brain time to catch up with the old brain. It is only after the new brain activates that a person can discern if there is actual danger.
There is a book out that talks about this phenomena and if not cared for, what the stress does to the body. It is great and I highly recommend it.