Periodically while watching “Midnight Family” you feel as if you can’t look at the screen for another second. But you can’t look away either. That tension encapsulates the push-pull of this documentary , a haunting portrait of a family of emergency medical worker s in Mexico City . Because as you tag along on another wild nighttime ride, and yet one more life-or-death race, the family’s careening ambulance seems like an emblem both of their reality and of your own whiplashing position as a viewer.

The family at its center, the Ochoas , own and operate one of the many private ambulances that serve Mexico City. The director Luke Lorentzen takes you right inside the ambulance, squeezing you in alongside the Ochoas and several others as they tend to traumatized victims and an occasional member of a patient’s family. It’s no surprise that it can be a deeply distressing fit. Nearly as alarming, though, are those instances when the Ochoas race a rival ambulance to the next accident and the documentary enters that unsettling zone where the pleasures of the chase (and good filmmaking) slam into your ethical sensibility, which is to Lorentzen’s point.

Your stomach may start jumping (your thoughts too) e ven before the movie and ambulance take off. After opening with some sober scene-setting — a man washing blood off a bright yellow stretcher — Lorentzen drops in some of the documentary’s few informational details. “In Mexico City,” reads text on a dark screen, “the government operates fewer than 45 emergency ambulances for a population of nine million.” Much of the city’s emergency health care, the note continues, is handled by “a loose system of private ambulances.” The Ochoas belong to this informal network, tending to hundreds of patients each year from inside their red-and-white ambulance.

Serving as his own cinematographer, Lorentzen spends a lot of time in the back of that van, a space that you settle into as workers and patients enter and exit. He regularly points the camera at the windshield, giving you front-row access to the chaos; every so often, he trains it on the rear-door windows, as if looking for an escape. Another camera, mounted on the top of the dashboard, enables you to see inside the van, where Fer, the Ochoa paterfamilias, is generally found riding shotgun beside one son, Juan, a 17-year-old with a meticulous fade haircut and the wheel skills of a NASCAR racer.