With dark seas churning around her and a helicopter thundering overhead, Leigh Hennessy sputtered and flailed wildly, gasping for air as the wind and waves thrashed her about.

Just as she began sinking under the water for what looked like the last time, Kevin Costner appeared above her and pulled her up to safety.

It might sound like a nightmare that morphs into sweet dreams. But for Hennessy, a Lafayette native who has worked as a Hollywood stuntwoman for almost a decade, it was just another day at work.

In recognition of her skills during those tense moments — the opening scene for the 2006 movie “The Guardian,” starring Kevin Costner and Ashton Kutcher — Hennessy earned a nomination for a Taurus World Stunt Woman Award.

She notes her work on “The Guardian” as among her proudest accomplishments in a career that has included stunting for everyone from Lucy Liu in both “Charlie’s Angels” movies to Helen Mirren (“Teaching Mrs. Tingle”), to serving as the sole stunt double for Demi Moore in the 1997 film “G.I. Jane,” about a woman who joins the Navy Seals.

Hennessy has bounced around in life — literally. Before getting into stunt work, she was a trampoline champion. She holds two world titles in the sport and is listed in the Guinness Book of World Records for winning the most U.S. National Championships of any woman.

But after a lifetime spent pushing her body to its limits — tumbling down stairs, diving off 90-foot buildings, jumping out of helicopters, leaping on trampolines — Hennessy, now in her 40s, began suffering from career-jeopardizing injuries this past spring.

“I had both my knees reconstructed during my youth, and over the years I began suffering from arthritis,” she said. “Finally, a few months ago, the pain in my knees became too much.”

Worried about what it could mean for her livelihood, Hennessy nonetheless made yet a different sort of frightening leap and took herself to the doctor. “He was shocked. He couldn’t believe I was still walking around,” she said.

In April, Hennessy underwent a total right knee replacement. Determined to get back into action as soon as possible, she started physical therapy the day after surgery. For three weeks a therapist came to her house and worked with her.

“It was about four to five weeks before I could drive,” she said.

Unlike the typical knee replacement patient, Hennessy had to get back to doing much more than just walking and driving. She put herself in the hands Robbie Banta at Touro Hospital’s Back in Action Center, which specializes in physical and occupational therapy.

Before becoming a physical therapist, Banta, a native of St. Gabriel, had spent years as a coach for high-level gymnastics.

“Because of my background I understood exactly what she was trying to get back to doing,” Banta said. “There was no translation necessary.”

Unlike most of Back in Action’s clientele, who Banta said tend to be older, Hennessy’s needs were very advanced and demanded more advanced techniques.

“With Leigh we did a lot of jumping and squatting,” he said. “We were working with a bigger range of motion and concentrating on developing more strength then our typical client needs.”

Two-to-three days a week for seven weeks Banta and Hennessy worked to get the stuntwoman back in shape.

“She didn’t take the process lightly,” Banta said. “She was very motivated and gave 110 percent, as I’d expect from an athlete.”

After almost two months, Hennessy walked out of the building for the last time in July and jumped right back in to a 10-day job doing driving stunts for the upcoming film, “Don’t Mess With Texas.”

Thankful for her new, pain- free right knee, Hennessy said the left knee can wait for now as she continues to regain her strength. “Before I did the surgery I asked the doctor if I would ever be able to jump on a trampoline again,” Hennessy said. “He said nobody had ever asked him that question before. I have the feeling I’m going to be the first one to let him know.”