There are four types of PTSD.

Acute stress disorder begins within four weeks of the traumatic event and lasts at least two days. If these same symptoms continue for more than four weeks, the diagnosis is changed to acute PTSD. While acute stress disorder presents itself within four weeks, PTSD can begin much later, even years after the trauma, as "delayed onset PTSD." After a period of 90 days of PTSD symptoms, the diagnosis changes again to chronic PTSD.