The moments, awkward and fleeting, started casually enough, little tickles of annoyance more than alarm. In 2000, in the middle of a Seder with my stepsons Nat and Simon, Mom called Nat “Nate.” He seemed surprised, hurt even. She didn’t remember his name? I growled at her about it, sotto voce, while we fussed over a serving platter. When she remained silent, I figured she was embarrassed.

At my brother Emmett’s wedding in 2004, she wore a lavender shirtwaist, its matching fabric belt consistently askew, revealing the elastic beneath. My mother has never been a stylish dresser (much to my sister Phoebe’s chagrin) but she has always been a fastidious dresser. Making sure that belt had loops to hold it in place was the kind of thing she would do automatically.

One night, she and my father saw a movie with friends, one I had already seen. I asked her opinion of a plot point, and it became clear she hadn’t followed the story. She changed the subject.

Like I said, little tickles. People misspeak—we actually had a relative named Nate. Errant belt loops on a wedding day might not be paramount to someone who doesn’t care about clothes. Not recalling a movie plot? I can’t remember the movie in question, myself.

But during the course of the next year, she didn’t seem quite right. She kept telling me she was tired, she who was famous for never taking naps. The family joke had always been that if she lay down in daylight, she’d need to be shot. Like a horse.

I bought a new dress, not fancy, what she and I would call a schmatta dress, to cook in, wear around the house. It was navy with three buttons beneath the collar, each of a distinctly different design. When she saw the buttons, she recoiled. “What’s wrong with that dress?” she shouted. “Why don’t the buttons match?”

“It’s the design,” I said. “They’re not supposed to match.” That didn’t mollify her. She stayed rattled, and although she didn’t say anything else, she continued to glare at both me and the dress.

I dismissed the incident at the time, but I have thought of it frequently since, her off-kilter reaction to something so small. I know now what I missed then. It was about order. The buttons weren’t uniform. And in her condition, suddenly that felt like chaos.

One day, Phoebe called me, distraught. A friend at work told her she’d logged on to a website where college students comment on their professors. Someone had posted a complaint about Mom. She was too old to teach. She had given the same lecture twice.

“Completely untrue!” I thundered. “You know it was just some kid who was failing, seeking revenge.” Phoebe knew no such thing, but we agreed never to mention it. We made it our secret. When Mom “decided” to retire a few months later, we knew it was not our secret at all.

By the following September, she was still tired, and I insisted we see a neurologist together. It turned out that she’d already seen one, Jesse Weinberger at Mount Sinai Hospital, the year before. He’d done those Doppler tests that determine whether or not your carotid arteries, a station of the cross of cardiovascular disease, are in working order. Once we were in his office, I learned that the results had been dicey enough to warrant retesting, but my mother never came back.

Was she actually sent a reminder card? I asked stiffly. Weinberger opened the file and showed me three dates on which three different cards had been sent. It didn’t surprise me that she would ignore them; she never put much stock in doctors and avoided them whenever possible. That she wouldn’t remember receiving the reminders, however, was unthinkable. Yet that’s exactly what she said. She didn’t remember.

Weinberger repeated the Doppler and discovered that one artery had closed completely; the other, 75 percent. This meant that my mother, the college professor, had 25 percent blood flow to her brain at this moment, which had been the situation for six months or more. That she had been teaching at all seemed astonishing.

I struggled to contain my panic, asking questions, taking notes. Keeping track. That had always been my job. Or at least I thought it was. When Weinberger asked her what medications she was taking, and which doctor had prescribed which pill for which illness, she hesitated. I leapt in authoritatively, starting to recite. Quite firmly, he asked me to stop; he was addressing my mother. She continued the list while I listened, feeling light-headed. She was naming doctors I had never heard of, medications I had no idea had been prescribed. Over the past couple of years, she had told me repeatedly that she was fine. Why hadn’t she told me the truth?

Weinberger instructed her to collect all the medications she was taking and bring them in. At the next visit, she placed two bulging plastic bags on his desk. There were easily thirty bottles of pills, mostly antidepressants in differing doses. When he asked her why she was taking them, she squinted at some of the labels, as if the answers would be written there. She made jokes and smiled coyly. She didn’t know.

I was equally baffled. When had this happened? Why hadn’t I seen it more clearly? Most importantly, how fast could we fix it?

Not fast at all. Tests and procedures, small and large, loomed. Each test led to another appointment, to another procedure. We sat side by side in endless waiting rooms. My mother had trouble filling out the forms. She couldn’t seem to make the pen move the way she wanted. On the first few visits, she recited her social security number by heart as I wrote it down. But when she started handing me her Medicare card, I realized she could no longer remember it. I filled out so many forms for her that when I saw a new doctor for myself the following year, I gave my birth date as 1931.

“Have you had any surgeries?” a technician asked her a few weeks after the one she had to fix the carotid artery that could still be salvaged.

“No,” she said.

“Yes,” I said.

“You make a good team,” he said.

As my mother began the torturous process of disappearing in plain sight, I retreated to my kitchen, trying to reclaim her at the stove. Is there any contract tighter than a family recipe? Just do as I say and poof! Here I am, good as new. Or something like that. Picking up a pot was not the instant panacea for illness and isolation and utter despair that I wanted it to be. But it helped. When I turned to the food, I felt grounded in my mother’s rules, and they worked every time.