You do want to have someone give you a ride.
You may want to check out www.tbilaw.com
to read the comments Attorney Gordon Johnson has to say about NeuroPsych Assessments (NPA).
I would also recommend having an attorney with expertise with concussion/mTBI and NPA's counsel you and review the intentions of the NPA. The wrong battery of tests can be detrimental to your future care.
And, do not try to prepare for the NPA. If you are anxious the night before and struggle to sleep, that is OK. It will only magnify your symptoms. Do not tell the tester if you could not get a good night's sleep unless asked specifically. Only answer questions asked. Do not try to volunteer information to explain your symptoms. Let the tests speak for you.
Do your best but do not try to accentuate anything. There are validity tests that will show if you are faking.
And, try to relax and go with the flow. You will be fine.
My best to you.