So, he thinks the negative MRI means you did not suffer a concussion?

Using a negative MRI to rule out concussion is not supported by any standards of medicine.

Some better analysis of possible PTSD issues would be worthwhile before starting a strong med like Cymbalta/Duloxetine.

There are other ways to treat PTSD besides just meds. Figuring out what your triggers for anxiety attacks are would be a good start. Meds just mask the symptom. Finding the cause would be worthwhile.

Have you ever had a brain injury or brain trauma previous to your recent concussion?