You have a standing tradition of going to church with your frail mother. Although in her late 80's she has no signs of illnesses.

It is custom that you always drive in back of her. To see her safely home. While your husband or wife takes your kids home. Then you stop and sit for coffee. This has been a tradition for over 15 years in your life. Place yourself with a bond that strong.

One day you are driving home on a two lane road. A 18 wheeler traveling at 65 mph veers onto your lane. It's speed causes the impact to throw both your mothers car and his trailer to the right side of you into a ditch. Before you can react you passed it by. After you stopped pass the accident site. You run to aid your mother. Her chest is crushed in and she is bleeding at the ears. Which shows internal bleeding. Her face is distorted you cannot give CPR. So all you can do is hold her, feel her gasp for breath and die in your arms. This is your mother that was not suppose to die. She had nothing wrong with her. More to the fact she did not deserve to die that way.

6 years down the road you are at a mall and a friend sees a dress. Makes a statement "your mother would have loved it". Those memories still haunt you and you break down and cry. But we understand that type of death. so they say "I'm sorry let's go have a drink to calm you down". Then they let you gain control of your emotional side. Sometimes one must actually leave as they are still suffering.

Now a Combat Veteran watching a movie that brings back memories. They break out crying and wanting to talk about it. But instead are hauled to the VA mental ward.

WHY?   Because their view of the death and destruction is not comprehendible to the one's here. Now another thing will happen out of that accident. Reality and Doctors will always tell you there was nothing you could do. But in your mind and nightmares. You will always see yourself "just" driving pass as your mother was hit. That it should have been you. It's the same thought process. Just some are more unthinkable that others.

A person who has PTSD learns to live and cope with it. The level is as severe as the traumatic experience was unthinkable (COMBAT). If that person is exposed to another trauma, that severely effects them, does that persons PTSD worsen?

No, One loves their mother with their whole heart. One loves their child with their whole life. When a person loses their mother, they feel dead, alone, sad; like life can't go on. They refuse to live for many months until they can come to terms with their grief. When one loses it's child? They feel their breath taken out of them. They have no need to get up in the morning. Their life is meaningless without their child. They hurt like they think they can never hurt again. Yet, They suffered the same pain process as the loss of their mother. It just  processed differently. Hitting many different painful sides that was not targeted at the loss of the mother.              

So, in conculsion. A person can have mutiple instances of PTSD, as one can have different sufferings of losses of their loved one's.