ABC News' Cecilia Vega reports:
Haley Dunphy, the big sister on "Modern Family," appears carefree, spending hours on her cell phone and giving her parents a rough time on the show like any other teenager.
But Sarah Hyland, the 21-year-old actress who plays Haley on the show, has had anything but a carefree life. Hyland's been struggling with kidney disease since childhood, when she was diagnosed with abnormal kidney development at the age of nine.
"I would be in a lot of pain a lot of the time. If I didn't get, like, 12 hours of sleep, It felt, like -- It felt, like, none at all," said the Manhattan-born actress.
A secret to the millions of "Modern Family" fans, Hyland would often sit down or text on her phone during a scene to hide her exhaustion.
"You know, if you're sick, you still go to work. And in between takes, you sit down, or you lay your head down or something," she said.
As the pain got worse, the actress began looking for an organ donor to avoid spending her life on dialysis. Luckily her father, actor Edward James Hyland, was a perfect match.
Last month, she underwent the transplant surgery and will recover this summer while the show takes a break from filming.
Actress Julie Bowen, who plays Claire Dunphy on the show, has been stopping by to help her clean. Her real-life and on-screen boyfriend, Matt Prokop, has been helping her recover as well.
Hyland offers hope and advice for those struggling with kidney disease: "Know that you're not alone. Even though it may seem like it a lot of the time. And that if you ask, 'Why me?' Well, why not you? You know? It makes you the person that you are today."
Hyland is a youth ambassador for the Lopez Foundation, where she helps to promote community awareness for organ and kidney donation.
For more information about Sarah Hyland's health struggle, pick up this month's Seventeen magazine.