Ben, I hope that is OK for me to offer you some CBT.

You wrote "continued brain deterioration". and "I feel severely brain damaged"

You also wrote "I was evaluated by a top neurologist who said I had no noticeable deficits. A few days ago I spoke with a top psychiatrist who said I sounded very intelligent and articulate and should consider becoming a psychologist for my career. My parents and gf say they have not noticed any drop off in my intellect and my friends have not mentioned anything about me acting differently besides that I am now more quiet."

In CBT jargon the first quotes are forms of a Negative Automatic Thought (NAT) called Catastrophising.

The key to CBT is to challenge a NAT, asking if there is any evidence for it.

The second quote shows that there is not a scrap of evidence that your NAT has any basis in reality.