The ones they give at most doctor's offices (including first visit to neurologist) are very simple but statistics show they are really effective. Nothing to do to prep but show up. IF they detect anything peculiar in those, they will do a number of other things and it may lead to a neuropsych eval. Those are lengthy but really show what, if any, particular areas/functions are having a hard time. I had one several years ago when I really felt like I was going off the deep end and was delighted with the results. I'm also happy I have that baseline for the future.
BUT when I asked two different doctors, years apart, in different states, about memory/confusion, both requested a B12 test. The first time it came back normal, and it turned out I was suffering from side effects of a harmless-seeming medication. The second time--this year--my B12 was low. I felt better and thought better within about three weeks of starting on the dosage recommended by the doctor. Just passing that on because of course we think we're losing our minds, right? Sometimes it's a simple thing. (The low B12 could be traced back to excessive Advil use, which lowers absorption of many nutrients but especially goes after the B12.)
Best wishes to you. It's scary and so many of us are going through this.