The woman lay slumped in a subway stairwell, so Jonathan Kleisner knelt to look her in the eye.

“We’re here to help, OK?” he said. “Can you tell me what happened?”

Someone had called 911 to report a woman having what appeared to be an epileptic seizure in the subway station at the corner of Seventh Avenue and West 12th Street. Arriving in his ambulance, Mr. Kleisner said he was doubtful about the diagnosis. This would be a drug case, he believed, a hunch soon confirmed by the half-dozen used needles scattered beside the patient.

The woman, who had collapsed in a fit of tremors minutes before, opened her eyes. She regarded the man before her — lean, all-business attitude, blue uniform exuding some kind of authority — and sprang awake. She placed both feet on the ground and rose with barely a wobble, muttering that she was OK. Then she turned and started up the stairs, unaware that she was walking away from one of the best-trained paramedics in the country.

For Mr. Kleisner, the case wasn’t much of a challenge. But it was still better than his old job working on Wall Street.

“We get a lot of nothing calls like this,” he said after he and his partner had packed up their gear. “But our bread and butter is big stuff. I’m talking amputations, people hit by trains, bodies in pieces. Catastrophic stuff.”