Put the book down. If it is any comfort - I also lose words. I have concocted the following scenario to explain it: I want a word. As I am searching for it my 'files' I come up against a drawbridge. It's raised. And on the other side of the vast, gapping waterway is My Librarian. She is smiling at me - waving the file I need & mocking me to come get it. I smile back and turn away. Soon the drawbridge will go down & I'll be able to walk right over there without ado. So fuck her.
If I compare myself to who I was - just even a few years ago - I can become mired in self analysis. My father & pretty much ALL his family suffered from a vascular dementia if they made it to their 80s. My grandmother, aunts, cousins all ended up with it. Instead, I live in My Now. Without comparison or dread.
I have never had a closed head injury - and as former nurse, I understand your concerns. But always remember - Medicine isn't so much a science as an art. Doctors base their proclaimations on their experiences and data from OTHER PATIENTS. Every Human is unique - and many times they don't fit into the medical course their doctors have pigeon-holed them into.
Live each day - with gratitude for the love in your world. Don't let anything rob you of your present moment. The future for any of us is never a given My Dearest Jack.
PS - I also suck at names and faces. My brain was hardwired when I was an OR nurse. At times, I can only recognize people who are wearing masks & have their hair in hats. The brain is really an incredible organ.