I am really slipping mentally now

So, I have been working at this job for 10 years.  It should be easy enough to complete my tasks.  Well, what was easy has been a bit of a struggle lately. Last week I was entering data on my clients, something that I do all the time.  I was figuring some numbers and don't know where I came up with the numbers I put in.  I entered some data on Friday afternoon and was actually "lucid" for lack of better term and figured out that I had been entering the wrong numbers all week. Well, it was late Friday, so I came to work yesterday morning and entered the correct figures on all the cases I worked on last week.   I do not have a clue how I came up with the numbers I entered.  I am thankful that I came to my senses and realized what I had been doing; but I wonder how often I have entered numbers that came out of left field.  I wonder how much longer I will be able to function in this job. Maybe it was just a small slip and won't happen again for a long time. Who knows!?
I have been doing little tests on myself lately.  Just things that I know the neurologist does.  I cannot stand with feet together and eyes closed without falling.  I cannot close my eyes and touch my nose. My finger always lands on my forehead.  I cannot walk heel to toe without falling.  Those are just some that I have done and cannot do well at all now.  I was able to touch the bridge of my nose with my eyes closed before.   All of these things are becoming much worse. Before, I guess they weren't definitive enough for the neuro, IDK what they will think now.