This topic center concerns mental and emotional problems people experience in the wake of 'trauma', where trauma is understood to refer to an event involving being a victim of or witness to atrocity, violence, true horror and/or the death of another or near death of ones self. Examples might include rape, murder, torture, accidents, terrorism, etc. DSM describes two trauma disorders: acute stress disorder, and posttraumatic stress disorder, both of which you may read about in the links to the left of this document. In a nutshell, acute stress disorder occurs in the time frame between just after exposure to a traumatic event to six months later, and posttraumatic stress beginning at the six month point and extending thereafter.
Please read more at the following link: https://www.mentalhelp.net/articles/introduction-to-post-traumatic-stress-disorder/