Characterized by a suite of symptoms that persist for at least three days and up to one month after a traumatic experience (same diagnostic criteria for "trauma" as listed above). The specific symptoms of the disorder vary across individuals, but a common feature is intense anxiety in response to re-experiencing symptoms (e.g., recurrent intrusive recollections of traumatic event) of the trauma.
Panic Disorder, and other mental disorders, should only be diagnosed by a medical doctor, clinical psychologist, or other trained health provider who has spent time with the teenager and has conducted a proper mental health assessment. Diagnoses are complicated with many nuances. Please do not attempt to diagnose someone based on the symptoms you read in magazines or on the internet. If you are concerned, speak to a trained health professional.
Neural circuitry involving the amygdala (which regulates emotions like anxiety and fear, stimulating the HPA Axis and sympathetic nervous system) and hippocampus (which is implicated in emotional memory along with the amygdala) is thought to underlie anxiety. People who have anxiety tend to show high activity in response to emotional stimuli in the amygdala. Some writers believe that excessive anxiety can lead to an overpotentiation of the limbic system (which includes the amygdala and nucleus accumbens), giving increased future anxiety, but this does not appear to have been proven.
If you are greatly afraid, however, such as being terrified that there is a burglar in your home that is about to harm you, the body produces a high degree stress response. We generally experience high degree stress responses as being anxiety attacks: where the changes are so profound they get our full attention. The greater the degree of anxiety and stress response, the more changes the body experiences.