I ran into this problem after salmonella at the age of 28. Cognitive decline occurred after some serious headaches. I had to re evaluate everything. I had to relearn how I took notes. I had to understand how I remembered things. I could no longer work as radial as I used to. And had to switch to linear mode. I had to break down tasks from "intelligent people only" mode to "anyone with a brain".

Of course there were other problems that prevented me from doing that like mental instability. But the whole process took a while. A couple of years.