What has happened to my memory?

This morning I went looking in my old checkbook transaction registries, trying to find out how much I paid for Cliff's Dell laptop last winter.  It's long-since paid for, but I just wanted to satisfy my curiosity.  
In the process of looking for that, I noticed that on December 23rd we had paid a plumber $615.  
"Cliff," I said, "Do you remember our needing the services of a plumber last December?"  
He wracked his brain, but couldn't remember our having plumbing problems at any time until just last week; and that only cost $25.  
See, December is traditionally a rough month for us.  We no longer spend money on Christmas gifts, but there's propane and personal property taxes and real estate taxes.  Believe me, I should remember having to pay $615 to a plumber in December.  As in, merry Christmas to me.  
My first recourse was to search back to that time in my blog.  Surely I would have mentioned something like that.  
But no; I simply babbled on and on about Christmas stuff and Pioneer Woman's cookbook and Santa Claus.  
I knew I wouldn't have a moment's peace until I found out what on earth that check I wrote to the plumber was all about, so I told Cliff, "This is going to make me feel like an idiot, but I am going to call the guy and see if he can tell us what sort of service we paid for."  
Well, the guy remembered me because we're the only folks from our town who have required his services.  
"Ma'am, I installed a water heater in the house out in front," he said, laughing.  
Oh, that.  No wonder I didn't remember; it was at the house where my sister-in-law lives, our old two-story house.  Wasn't MY problem... except for paying the bill.  
Still, there was a time when $600 would have thrown us into a black hole of debt for at least six months.  I guess times have gotten better.