Maybe I misunderstood you.

Is something shocking about saying it could be "aging"?

It happens to me from time to time. I lose track of a day here and there. I don't forget what I did, it's just that the day names are less significant lately. If you were working to a schedule or had appointments or needed to know what day it was I'm sure you would.

If I lost track of what I was doing for a day or two then I'd worry more.

Do you remember what you did on Saturday???