The first time your dad forgets who you are, annoyance might supplant sadness.

We were going into Costco to replace his lost hearing aid. Shoppers for the holidays raced about, all of them surly. So was the girl in the Santa hat, checking cards at the door. I scanned our card and had my dad sit down while I went back out to get an electric cart. A kind employee showed me how to work the controls after he saw me back into the building.

When I came back in the cart, Santa Hat Guard made me scan the card again.

I parked the cart in front of Dad, who said, “Oh thank you; now I just need to wait for my daughter.”

We were in a high stress situation. That’s more or less what accelerates the Alzheimer’s in certain moments, for lack of a simpler explanation. Being in a different place, not knowing the rules, pushes harder on what’s left and breaks it up faster.

I held up his hearing aid box. “Ready to go do this?”

He smiled. “Yep, just gotta wait for my daughter and then I’m ready.”

I thought for a second, went outside, and came back. Santa Hat glared at me. I swiped my card. Again.

“Ready to go, Dad?” I said cheerfully.

“There you are. I wondered where you’d gotten to.”

A lovely woman works at the Hearing Aid department: Dani. She taught him slowly and steadily how to keep the device in his ear. When they finished, he wanted to buy a big screen TV.

We already have a big screen TV.

We got eggs, and the cashews he likes. We left the scrum of shoppers and screech of carols over the loudspeaker. And as he hauled himself into the car by the door handle, he said, “I need pop tarts.”

We went to Walmart, where they were also kind to him. Found him a cart, kept him company when he announced, after we’d checked out, that he also needed Pepsi. I ran back and got it while the nice lady in the Santa hat and blue vest and Grinch onesie (they were having PJ employee day) kept him company.

On my way back with the Pepsi, a sudden balloon of red and black plaid wriggled backwards from a narrow crack in a display of pie-making supplies, and turned into a human behind. Standing upright, the filled-out plaid pants became a human with cute pony tails in a two-piece buffalo plaid. She grinned at me, looking very like an elf who had just successfully fought a chimney.

For no reason whatsover, I said, “My dad forgot my name.”

She blinked once, then shrugged, “Prob’ly so he won’t hafta buy you a present. He’ll remember it by New Year’s.”

I had to laugh. She patted me on the shoulder as I walked on by, then slid her red-and-black flanneled body between cans of condensed milk and assorted spices once again.

Dad was waiting with Santa Hat Nice Grinch Lady.

“There she is!” Ms. Grinch pointed, smiling, “See, you’re going home for Christmas!” To me she said with a wink, “He was a little worried you’d forgotten him.”

“How would I forget you?” I said to him. “You’re my dad.”