First, a Neuro-Psychologist Assessment (NPA) is very expensive. It is very difficult to get it covered by insurance if you have any now.

Second, a good NPA will only tell you what your current condition is. This can be helpful as a confirmation of your condition but will not usually lead to any better treatment. It can lead to better planning of tasks and activities. If you are told you have very poor short term memory, you can learn some work-arounds.

You complained.. <Honestly his favorite sentence was "Well... We don't know much about brain trauma".>
Your GP was being truthful with you. Current medical knowledge about concussion suggests treating the symptoms.

Other than diagnosing and treating issues such as a neck injury, there is not much that can be done by the doctors. There are Occupational Therapists who can teach you coping skills and work-arounds.

The biggest problem is we are the invisible wounded. All of our struggles and symptoms are invisible and subject to our own interpretation. This leads some doctors to saying we are making them up to get attention or whatever. Hypochondriac and somatoform are not uncommon terms they use to describe us.

What specific symptoms are you struggling with now?

What are your current capabilities and limitations?
Activities of Daily Living (ADL's) and work capabilities?

What do you hope to achieve from the NPA?