'Like I was watching a horror film': Shawn Johnson on her stalker’s attempt to allegedly abduct her in 2008, and how it has affected her life since “It made me look over my shoulder...It just made me question everything.”

It’s been ten years since a man was caught in what police believe was an attempt to abduct Olympic gold medalist Shawn Johnson, and she told ABC News it still haunts her.

“I have been driving down the street before, and paranoid that the yellow car behind me has been following me for too long,” she said. “I have been walking down the street and if someone even resembles Robert O'Ryan, I go into just a cold sweat.”

Thirty years after the death of actress Rebecca Schaeffer at the hands of her stalker, Johnson is speaking out about women in the public eye still facing harassment and the threat of violence every day.

Watch the full story on "20/20" THIS FRIDAY, April 12, at 9 p.m. on ABC.

Johnson captured the hearts of Americans in 2008 when her gymnastics skill in Beijing won her four Olympics medals -- three silver and one gold. She was 16 at the time.

Soon after, she had the opportunity to compete on one of her favorite shows, “Dancing with the Stars.”

Johnson told ABC News she was “such a reserved… and just sheltered 16-year-old” at the time.

“I hadn't been up close to a guy, and here's [professional dancer and choreographer] Mark Ballas, and he's like, ‘Okay, we're gonna learn how to ballroom dance and be very close and intimate.’ And I remember being just like, ‘Oh my gosh,’” she remembered.

Across the country, at the same time, a 34-year-old Robert O’Ryan was becoming obsessed with her as he watched her performances from his trailer in Florida.

For Johnson, the morning of March 25, 2009, was just like every other day on the show.

“I remember getting ready for the day, being dropped off at the studio, and it just feeling normal,” Johnson said. “I was just giddy and on cloud nine being able to be there for another dance and another week.”

O’Ryan’s dangerous obsession led him to decide to drive across the country to confront her on the set of the show in Los Angeles.

Days before his arrival, he was stopped by police in Alabama. In a conversation captured on police dash cam, he told police of his intentions to meet her, saying they have a future together and will get married.

The police issued O’Ryan two tickets, one for not having insurance and another for an expired license plate.

"I know if sounds a little bit crazy, but my intuition tells me that we're gonna have a beautiful relationship together," O'Ryan told the policeman.

During the 29-minute stop, O'Ryan mentioned Johnson at least three times.

O’Ryan continued onto Los Angeles, arriving at the studio as Johnson was preparing for the show, completely unaware of his existence and his alleged intentions.

“I remember people acting strange,” Johnson said. “We are all on the floor, and it was a rush to get me back into the red room. And I was like, ‘Okay, this is strange. Am I getting voted off? Did I do something wrong? What's going on?’”

She said she was told to go back to her trailer, where she found FBI agents and her parents, her mom crying.

“Mark is in there, and he's livid, just fuming,” she remembered. “I remember the FBI agent was the first one that started talking, and they said, ‘We need to tell you. You have a stalker. We weren't aware of it, but we are now.’”

“‘He broke onto the set. He broke onto the stage. He was tackled on the stage. He was arrested and taken off property. He's being held in custody,’” Johnson remembered being told.

Authorities found zip ties, duct tape, guns and knives in O’Ryan’s car. They also found love letters in which Johnson’s name was hyphenated with his.

O’Ryan told police he had no intention of harming Johnson, but that he would have killed anybody who got in the way of their being together.

“They said that he had handwritten letters to me, and love notes. And that this whole plan he had constructed to essentially abduct me, not to harm me,” Johnson said. “He, in his state of delusion, thought that I was the mother of his unborn children, at 16, and he would never harm me. But he was going to kill anyone that got in the way.”

“Think of yourself at 16,” she said. “I could barely process geometry, let alone process this thing and this event that happened that I didn't witness.”

Johnson said it was “surreal… like I was watching a horror film.”

“I was very aware of risks and liability with fame. But, this was kind of to a whole new level,” she said.

She said over time, she started to understand that O’Ryan’s security breach “almost opened up a floodgate of every other person in the world.”

“It made me look over my shoulder when I was walking down to the grocery store. It just made me question everything.”

Johnson shared that she had to get a different car, move homes, use different names, use a different cell phone and hire a full-time bodyguard.

“I remember walking home, and being so traumatized and so terrorized by the idea of the what ifs that I couldn't even get myself to go home,” Johnson said.

Then, one year after he was charged with a felony charge of stalking and two misdemeanor counts of carrying a loaded firearm in a vehicle, she had to testify against him in court.

“The first time I heard every detail of his master plan, every detail about him getting pulled over before he ever made it to California, was when I was actually in court and I had to face him,” Johnson shared. “That was probably, for me, more traumatizing than the actual event just because he never made it to me. It was almost like I had lost the fight because I had to… relive it to a certain extent.”

She remembered asking “How is this fair?”

“He didn't succeed in his plan in abducting me, and he never got the satisfaction of seeing me in person. And for the court to allow him that satisfaction, to sit in front of me for five hours and just stare, I felt so just, dirty, and I was angry and livid,” Johnson said.

O’Ryan was sent to a mental institution by the judge, where he spent five years.

She said that soon after she testified against O’Ryan, her decision to share so much of her life on social media “was strategy -- I wanted the world to see that I had moved on.”

“I wanted the world to know that I was living my life. But, the places I was saying I was, it wasn't accurate. I was posting a picture again of me at the Grove in Los Angeles, but it was a picture from four days prior,” Johnson said. “I was trying to put on a facade that I had moved on when I really hadn't, but I was trying to convince myself that I could as well.”

Seven years after the stalking incident, Johnson got married. She and her husband and decided to share their life online, where she said “we chronicle our life for the world, and show them all of the glamour and terribly not glamourous things about our life.”

O’Ryan is now out of the institution, and the thought of another encounter still haunts Johnson.

In Schaeffer’s case, her murderer is still in prison and will likely stay there. For Johnson, her stalker is forbidden from finding and meeting her -- but the possibility exists he may still try.

Johnson said she doesn’t want to ever feel like she has “let him win.”

“When I post a new YouTube video saying, ‘This is what I'm doing, it's just a little piece of victory for myself that says, ‘You didn't take it from me, and you never will.’”