Nearly eight years ago, Sia Cooper couldn’t wait to become a better version of herself, thanks to her new breast implants.

“It gave me confidence,” the 29-year-old fitness trainer and Instagram model @diaryofafitmommyofficial tells The Post. But the new Sia Cooper didn’t last long.

“My health started changing for the worse.”

Believing she was suffering from “breast implant illness” — a controversial and theoretical autoimmune disease which sufferers believe is caused by silicone implants — Cooper eventually decided to have her implants removed.

“I thought fatigue, hair loss, acne — these things were normal [new] mom things,” says the Florida mother.

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Each year, she says, “I [felt] worse than I did the year before.”

She’d experience facial and abdominal rashes, brain fog, chest pain and joint inflammation so bad she couldn’t lift weights anymore. Eventually, she was losing hair “in clumps” and sleeping 12 to 14 hours a day.

She’s had nonstop blood tests, X-rays and doctor consultations, with results always normal, negative of any conditions.

“I felt so helpless.”

Recently, in a post unrelated to her mysterious symptoms, she divulged to her inquiring Instagram followers that she had breast implants. They responded with comments about breast implant illness.

“It planted a seed in my head,” she says. “Maybe this is it.”

While the FDA does not recognize a breast implant illness (BII) diagnosis, it also states on its website that BPI cannot be entirely dismissed without “much larger and longer” studies. (It also notes a “low but increased likelihood” of being diagnosed with anaplastic large cell lymphoma (ALCL), a cancer of the immune system.)

Dr. Daniel Maman, of Manhattan-based 740 Park Plastic Surgery, says Cooper’s symptoms are exceedingly rare and there’s “no medical justification” for them.

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“Breast implants are the most studied implanted medical devices in the world,” Maman tells The Post. “There has never been a scientific study in any credible medical literature showing an association” between autoimmune diseases and breast implants, “period.”

“There are women certainly that have these unexplained illnesses and then miraculously get better once the implants are removed,” he admits. “But there’s always a placebo effect.”

Cooper — who has no family history of autoimmune diseases — also decided to see the cosmetic surgeon who gave her the implants. In tune with Maman and a majority of their community, he told her there’s little evidence to support BII.

Cooper knew there was no assurance a breast “explant” would help, but, she says, “I was willing to try it.”

Less than two weeks ago, she traveled from her home in Destin, Fla., to Newport Beach, Calif., to have her implants removed by Dr. Jae Chun — a cosmetic surgeon popular in the explant community for his support of these claims. The surgery cost about $7,600 — about $2,100 more than her implants cost in 2011.

“I [can] take a deep breath for the first time,” she says, even with her mending chest. Her posture has improved, inflammation and acne are subsiding, and she’s had a boost of energy. “I have been so productive . . . My body just feels better.”

“I took my doctor for his word,” says Cooper, who wishes she’d asked more questions before getting the implants.

“I just want women to educate themselves — which is something I did not do,” she says. “Do your own research. Be your own health advocate.”

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