By Stephanie Stahl

PHILADELPHIA (CBS) — It’s an illness caused by certain kinds of exercise that are often mistaken for muscle soreness. But if it’s not treated quickly it can lead to life-threatening organ failure.

It’s called rhabdomyolysis and it happened to a Delaware County woman at the worst time imaginable.

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Niki Kusner was ready to get married.

She had dreamed about her wedding her entire life. But the magical day she had planned for almost didn’t happen.

Niki and her fiance Mike had carefully planned every detail for a year.

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But days before the nuptials, Niki ended up in the hospital.

“I was hysterical and crying,” she said recalling that day.

“It was very scary, really scary,” said her fiance Mike. “I was thinking she was dying.”

It was after a challenging spin class when things started going haywire for Niki.

“I never thought something like that would happen to me,” she said. “I’ve played sports my whole life and I’ve done intense training and all that.”

Niki who was a soccer player at Temple University suddenly developed a condition that strikes athletes.

It’s sometimes mistaken for the flu or just soreness after a workout.

“We see it in people after intense exercise,” says Dr. Ed Cikowski a Springfield internist.

Nike was diagnosed with rhabdomyolysis.

The condition occurs when muscle, for an unknown reason, breaks down and releases toxins that can cause kidney failure.

“She worked out her whole life and then all of a sudden a week before the wedding she’s hurt because she worked out,” said Mike.

It starts out with sore and weak muscles and then there’s swelling.

“My thighs, both of them from my knees to my thighs were 10 times their size,” said Niki.

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At Riddle Hospital, Niki got the standard treatment of intravenous fluids to remove the toxins but her levels weren’t going down fast enough.

“It got to the point where I may not be going to the wedding and then that’s when I couldn’t handle it anymore,” she said.

So the staff decided to surprise Niki with a rehearsal dinner at the hospital.

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She was overcome with emotion.

“The hospital did an amazing job,” said Mike.

The hospital staff did something else on the day of the wedding.

They allowed Niki to leave for a few hours to get married.

“It was the right thing to do,” said Dr. Cikowski.

Even though she didn’t feel good, Niki, who made a beautiful bride that day, got married as planned.

“I couldn’t really walk and I couldn’t stand for long period of time,” she said. “It’s a once-in-a-lifetime thing and you’ve been dreaming about it your whole life and then you can’t even dance.”

After the wedding on New Year’s Eve, Niki went back to the hospital for more IV therapy.

Even though she’s recovered and is happily reminiscing about the wedding, Niki says she’s worried about working out again.

“I didn’t feel any pain, I didn’t feel anything when it was happening, it was afterwards,” she said. “So how do I know it’s not going to happen again?”

Doctors say the syndrome is rare and that working out is beneficial.

But there’s no way to prevent rhabdomyolysis except to stay hydrated.

That’s why awareness and quick treatment are so important.

“As people do crossfit you know, cycling classes, and there are more intensive forms of exercise I think we have to be more aware of it, understand that it’s a consequence,” says Dr. Cikowski.

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It’s a lesson learned for the Delaware County newlyweds who are together through sickness and health.

Stephanie Stahl