Symptoms of this disorder vary by individual. There is usually an anxiety response where the individual re-experiences the traumatic event. This can occur through intrusion symptoms, negative mood, dissociative symptoms, avoidance symptoms, and arousal symptoms. Many of those with acute stress disorder suffer the inability to feel positive emotions but feel strong negative emotions (sadness, guilt, etc). Another common symptom is dissociative amnesia (forgetting moments of the event) and many suffer with sleep onset and maintenance issues. Other common experiences include irritable behavior (can lead to aggressive verbal or physical behavior with little or no provocation), difficulty concentrating, reactions to unexpected stimuli. In order to be diagnosed as acute stress disorder, symptoms must last for at least 3 days to 1 month after the traumatic event.