The most characteristic manifestation of PTSD is the recurrence of various forms of intrusive traumatic re-experiencing (pathological re-experiencing) after a major traumatic event. Patients often experience this “repetitive experience” in a very clear and extremely distressing manner, including repeated re-experiencing of the traumatic event (flashback) in the form of illusions and hallucinations (fantasies). In this case, the patient seems to be fully present again at the time of the traumatic event and re-expresses the emotions that were associated with the event. Patients often experience intense psychological distress and physical reactions when they are exposed to events, situations or other cues that are related to or similar to the traumatic event. Patients frequently have dreams (nightmares) with very clear content that are clearly associated with the traumatic event. In the dream state, patients also have recurrent scenes closely related to the traumatic event and produce emotional experiences similar to those at that time. Patients often awaken from the dream and continue to actively “continue” the “interrupted” scenes after waking, and have intense emotional experiences. After a traumatic event, the patient adopts a persistent avoidance attitude toward trauma-related objects. The avoidance includes not only specific scenes, but also related thoughts, feelings and topics. Patients are reluctant to mention the event, avoid conversations about it, and even experience “selective amnesia” about it. Patients seem to want to “erase” these “traumatic events” from their memories. After the traumatic event, many patients also suffer from “emotional paralysis”. Externally, the patient may appear to be indifferent, indifferent, distant, unfriendly, afraid, guilty, or unwilling to interact emotionally with others. Patients themselves feel that it is difficult to take interest in anything, and activities that they used to be passionate about do not stimulate their emotions. Patients feel distant, isolated, or even out of place from the outside world, have difficulty accepting or expressing delicate emotions, lack thinking and planning for the future, and are at the mercy of fate. In addition, some patients show symptoms of hypervigilance such as sleep disturbance, irritability, easily frightened, and inattentiveness. Most patients develop the symptoms within a few days to six months after a traumatic event, and usually return to normal within one year, while a few patients can last for many years or even for life.