Acute Stress Disorder
Acute Stress DisorderAcute Stress Disorder is a caused by trauma (traumatic stress) and lasts at least 3 days. The DSM-5 manual states that stressful events which do not include severe and traumatic components do not lead to Acute Stress Disorder; Adjustment Disorder may be an appropriate diagnosis.
Acute Stress Disorder explained
Acute Stress Disorder develops after exposure to one or more traumatic events, e.g., exposure to war (both civilians and military personnel), rape or sexual violence, physical attack, mugging, childhood physical or sexual violence, kidnapping or being taken hostage, terrorist attacks, torture, nature disasters and severe accidents. Many other causes of trauma are possible. 
Note: The International Classification of Diseases refers to Acute Stress Reaction,  which is slightly different and results from an "exceptionally stressful life event" or "continous trauma", and typically lasts between a few hours and a few days.  Both Acute Stress Disorder and Acute Stress Reaction have symptoms which are similar to Posttraumatic Stress Disorder.
Acute Stress Disorder DSM-5 Diagnostic CriteriaCode 308.3
A. Exposure to actual or threatened death, serious injury, or sexual violation in one (or more) of the following ways:
- Directly experiencing the traumatic event(s).
- Witnessing, in person, the events(s) as it occurred to others.
- Learning that the traumatic events(s) occurred to a close family member or close friend. Note: In cases of actual or threatened by death of a family member or friend, the events(s) must have been violent or accidental.
- Experiencing repeated or extreme exposure to aversive details of the traumatic event(s) (e.g., first responders collecting human remains; police officers repeatedly exposed to details of child abuse). Note: This does not apply to exposure through electronic media, television, movies, or pictures unless this exposure is work related.
- Intrusion symptoms
- Recurrent, involuntary, and intrusive distressing memories of the traumatic event(s). Note: In children, repetitive play may occur in which themes or aspects of the traumatic event(s) are expressed.
- Recurrent distressing dreams in which the content and/or affect of the dream are related to the events(s). Note: In children older than 6, there may be frightening dreams without recognizable content.
- Dissociative reactions (e.g., flashbacks) in which the individual feels or acts as if the traumatic event(s) were recurring. (Such reactions may occur on a continuum, with the most extreme expression being a complete loss of awareness of present surroundings). Note: In children, trauma-specific reenactment may occur in play.
- Intense or prolonged psychological distress or marked physiological reactions in response to internal or external cues that symbolize or resemble an aspect of the traumatic events.
- Negative Mood
- Persistent inability to experience positive emotions (e.g., inability to experience happiness, satisfaction, or loving feelings).
- Dissociative Symptoms
- An altered sense of the reality of one's surroundings or oneself (e.g., seeing oneself from another's perspective, being in a daze, time slowing.)
- Inability to remember an important aspect of the traumatic events(s) (typically due to dissociative amnesia and not to other factors such as head injury, alcohol, or drugs).
- Avoidance symptoms
- Efforts to avoid distressing memories, thoughts, or feelings about or closely associated with the traumatic event(s).
- Efforts to avoid external reminders (people, places, conversations, activities, objects, situations) that arouse distressing memories, thoughts, or feelings about or closely associated with the traumatic event(s).
- Arousal symptoms
- Sleep disturbance (e.g., difficulty falling or staying asleep, restless sleep)
- Irritable behavior and angry outbursts (with little or no provocation) typically expressed as verbal or physical aggression toward people or objects.
- Problems with concentration
- Exaggerated startle response
D. The disturbance causes clinically significant distress or impairment in social, occupational, or other important areas of functioning.
E. The disturbance is not attributable to the physiological effects of a substance (e.g., medication or aocohol) or other medical condition (e.g., mild traumatic brain injury) and is not better explained by brief psychotic disorder." 
ICD Diagnostic Criteria
The most recent approved version of the International Classification of Diseases, the diagnostic guide published by the World Health Organization is the ICD-10, published in 1992. The draft ICD-11 criteria for Acute Stress Disorder gives this description:
ICD 11 draft - Acute Stress Reaction
"Acute Stress Reaction refers to the development of transient emotional, cognitive and behavioural symptoms in response to an exceptional stressor such as an overwhelming traumatic experience involving serious threat to the security or physical integrity of the individual or of a loved person(s) (e.g. natural catastrophe, accident, battle, criminal assault, rape), or an unusually sudden and threatening change in the social position and/or network of the individual, such as the loss of one's family in a natural disaster. The symptoms are considered to be within the normal range of reactions given the extreme severity of the stressor. The symptoms usually appear within hours to days of the impact of the stressful stimulus or event, and typically begin to subside within a week after the event or following removal from the threatening situation."  Last updated November 2014.
Alternative terms for Acute Stress Reaction include Acute: crisis reaction, Acute: reaction to stress, Psychic shock, Combat fatigue and Crisis state. 
ICD 10 Diagnostic CriteriaCode F43.0
Acute Stress Reaction
"A transient disorder that develops in an individual without any other apparent mental disorder in response to exceptional physical and mental stress and that usually subsides within hours or days. Individual vulnerability and coping capacity play a role in the occurrence and severity of acute stress reactions. The symptoms show a typically mixed and changing picture and include an initial state of "daze" with some constriction of the field of consciousness and narrowing of attention, inability to comprehend stimuli, and disorientation. This state may be followed either by further withdrawal from the surrounding situation (to the extent of a dissociative stupor - F44.2), or by agitation and over-activity (flight reaction or fugue). Autonomic signs of panic anxiety (tachycardia, sweating, flushing) are commonly present. The symptoms usually appear within minutes of the impact of the stressful stimulus or event, and disappear within two to three days (often within hours). Partial or complete amnesia (F44.0) for the episode may be present. If the symptoms persist, a change in diagnosis should be considered." 
Alternative terms for Acute Stress Reaction include Acute: crisis reaction, Acute: reaction to stress, Psychic shock, Combat fatigue and Crisis state.