Acute stress disorder is a short-term anxiety disorder triggered by a traumatic, life-threatening event that causes a reaction of fear, helplessness, or horror.
Symptoms include feeling numb, reliving the event through disturbing memories or dreams, and avoiding anything that may be a reminder of the event. Symptoms are so intense that they disrupt daily activities like going to work and interacting with other people. The disorder may begin as soon as 2 days after the event and can last up to 4 weeks. Symptoms that last longer than 1 month are called post-traumatic stress disorder.
WebMD Medical Reference from Healthwise