PTSD is defined as a group of symptoms that may occur in response to experiencing or witnessing an event in which life was taken, (or threatened to be taken), or an event that caused significant psychological shock. Historically known as Shell Shock. 

Symptoms may include:
Nightmares
Flashbacks
Anxiety
Depression
Inability to focus
Hypervigilance
Difficulty discerning flashbacks from reality

These symptoms, if not treated, may lead to deterioration of daily functioning or suicide.