Since the hospital only said that I had a minor concussion with no other follow up to my doctor, can go after them now that I can no longer work?

I was in a car accident in 2005 and was thrown throughout the vehicle and found unconscious. I was rushed to the hospital and they sent me home 2 hours later saying I had a minor concussion. Three months ago, I noticed I couldn't remember things and I was getting confused. I couldn't even remember how to turn off my car. I went to a doctor and after a PET scan, blood work, Neurological tests and an MRI the results showed brain trauma. On top of that, they also found evidence of MS and the MS is attacking the brain trauma. I am now on disability and can't work because it is progressing so fast because of the trauma. They are calling it CTE. I would think that I could have had some therapy or anything done in the past 9 years to avoid what is happening to me.