(NewsNation) — It was hard enough when Lauren Sisler got a phone call from her father, who said that her mother had died and to get on the next plane home to Roanoke, Virginia.

When she arrived, it wasn’t her father who greeted her at the airport. It was her uncle, who told Sisler that her father had also died.

“It was just shocking. We had no idea that both of my parents were struggling with this addiction that could be so fatal and take both of their lives,” Sisler told NewsNation’s “Elizabeth Vargas Reports.”

She said both parents had undergone major surgery and were prescribed painkillers afterward. When OxyContin didn’t work, a doctor switched Sisler’s mother to fentanyl suckers.

“It was something that ultimately took both their lives within a few hours of each other,” she said.

In hindsight, Sisler says she thought about times when her father would fall asleep on the couch as they watched TV as a possible hint of the problem. Later, she noticed that her parents’ finances were in distress.

“All those things just start to add up over time, and I think ultimately that’s what led them down the dark road that they went on,” she said.

Sisler faced her own darkness as she refused to accept what had happened. She said it was 10 years before she looked at the toxicology reports on her parents.

“Somewhere, I had learned ‘respiratory failure.’ So I used to say ‘my mom died of respiratory failure. My dad died of a heart attack’ because it sounded so much better than overdose and addiction,” she said.

“Ultimately, my mom did die of respiratory failure, but it was because she ingested a lethal amount of fentanyl. I didn’t want the outside world to know what had happened to them and that, ultimately, addiction took their lives.”

After years of trying to protect her parents’ legacy, Sisler tells their story in her book “Shatterproof,” which goes on sale October 1.