Final answer:
The student likely has acute stress disorder, which is characterized by anxiety and disruptive recollections starting within four weeks of a traumatic event, such as the described car accident and concussion.
Step-by-step explanation:
The 25-year-old female student who presents with difficulty concentrating, night terrors, and a fear of driving following a car accident and hospitalization for a concussion and broken ribs is likely experiencing acute stress disorder (ASD). ASD occurs within a month of a traumatic event and includes symptoms like disturbing memories, flashbacks, anxiety, and sleep disturbances. These symptoms can cause significant distress or impairment in social, occupational, or other important areas of functioning. Given that these symptoms have begun within the last 18 days, ASD is more fitting than post-traumatic stress disorder (PTSD), which is diagnosed after symptoms persist for more than a month.