I remember only one pose from my first yoga class seven years ago: a modified seated forward bend known in Sanskrit as Paschimottanasana. I sat on a mat with my legs slightly bent in front of me, my arms wrapped beneath my thighs as my forehead reached toward my toes. It was about an hour into class, and my body felt like a stuck door slowly easing open.

A warm current of something—call it blood, call it chi—coursed from shoulder to shoulder. I felt the muscles unfurling from my spine; then, in the other direction, the vertebrae unsticking from each other—click, click, click. It was a sensation of freedom and release I remember as vividly as the first time my husband touched me. This was how I was supposed to feel.

Years of hunching over my computer had left me stiff, almost breakable. One false move—getting out of bed too quickly, tying my shoe—could lay me flat on a heating pad for days. Friends and family commented that my shoulders were rounding, my back curving, my chin protruding beyond my chest. Sometimes I'd see little old ladies hobbled over canes, their tiny bodies twisted and contorted, and I'd wonder, Will that be me?

Now I knew it wouldn't. After a series of yoga classes, I gradually began to stand up straighter and move through the world more easily without hurting myself. If the hunch in my back was a measure of how hard I was working at my job, my new upright alignment served as testament to how hard I was working on myself. Yoga had become my salvation.

Until it became my damnation.

In 2005, I was at my first yoga class in quite a while, as my busy life had been getting in the way of my routine. I took a class open to all levels; after all those years of doing yoga, I didn't think to reenter with a beginner class that took things more slowly. That would have felt like a demotion of sorts, as if I'd been put back a grade in the middle of the school year.

The class went fine until we neared the end. The teacher directed us into Plow pose (Halasana): on your back, balancing hips over shoulders while your toes touch the floor behind your head. If done properly, Plow pose has the power to straighten your shoulders and lengthen your neck; at least, that's what it always felt like to me. I remember exalting in the tension release across my upper body, the liberation of muscle from bone that through my practice I had grown to depend on, almost addictively.

Then I felt the throbbing. It started at the base of my skull, like a slow burn crackling down my neck. Within a week, I couldn't toss a tennis ball before a serve or pick up one of my baby cousins. My husband had to carry my weekend bag. After a few weeks, I went to a sports medicine specialist to see what I'd done to myself. We looked at my MRI together. "This mass right here is a bulging disk. It's pinching your nerve, which is why you're having pain down to your fingers," said Jordan Metzl, M.D., a sports medicine physician at the Hospital for Special Surgery in New York City. That Plow pose was likely to blame. "Your disk could have been bulging before," Dr. Metzl said, noting that premature osteoarthritis (something I'd had no idea I had) was weakening my neck and spine. "But hyperextending your neck while putting weight on it most likely made it bulge even more, which pinched your nerve."