“She was sitting in a recliner next to me when her head tilted back a little and her eyelids started to flutter,” Ms. Flanagan said. “One eye was drooping a little. I held her hand and said, ‘Are you OK?’ There was no response at all.” Then, a couple of minutes later, “she was back.”

Before, when their mother was still able to make such decisions, she had signed a do-not-resuscitate order and an advance directive instructing that “she didn’t want her life prolonged,” her daughter said. The family agreed that taking her to a hospital would only cause fear and disorientation. She and her siblings decided not to call 911.

Maggie Flanagan’s doctor said that she had probably experienced a T.I.A.; she had a more serious stroke five months later and died the following year, at home in her Chicago apartment.

But most people choose treatment. Ms. Splawn, the dog owner from Texas, said she was feeling fine and expected to go home to Petunia shortly.

Patients treated appropriately for minor strokes will remain at a higher-than-normal risk for another stroke, especially in the first year, Dr. Saver said. But “by two or three years out, the risk is just a little higher than for folks who never had a T.I.A. or a minor stroke.”

Wanda Mercer, for example, had a minor stroke four years ago, at age 66. An administrator at the University of Texas, she had donated blood during her lunch break, then fainted in an Austin restaurant. The staff called 911, but in the emergency room, everything seemed normal; she went back to work and regaled co-workers with her noontime adventure.

Suddenly, “I couldn’t find my words,” Dr. Mercer said. “I couldn’t articulate.” The problem lasted only seconds, but colleagues recognized a possible stroke and sent her back to the emergency room, where an M.R.I. revealed tissue damage. She has taken a statin, a cholesterol-lowering drug, and aspirin ever since.

“I’m lucky,” she said. “I haven’t had one adverse symptom since.”