DEER PARK, N.Y. (PIX11) — When Olivia Vilardi-Perez begins the first day of classes every year at Deer Park High School, she has a message for her teen students about resilience.

“Hey, this is what happened to me when I was 10 years old,” the now 32-year-old teacher said she explains to her class. “Your world can quite literally crumble beneath you, and you’re going to keep going.”

Vilardi-Perez recalled being in her fifth-period orchestra class on Long Island, as the first or second chair violin, when she noticed students getting pulled out of the room on Sept. 11, 2001.

One of the teachers mentioned something had happened at the World Trade Center in Lower Manhattan.

“You just know,” Vilardi-Perez recounted. “And it hit like a ton of bricks.”

Vilardi-Perez explained that her father, Anthony Perez, was working on the 103rd floor of the North Tower in the offices of Cantor Fitzgerald, a large financial firm. More than 600 employees perished with him.

“He had a wake,” Vilardi-Perez remembered. “I hid in the closet in the basement of the funeral home. Faculty members came, and I went to school the next day.”

Vilardi-Perez said she felt “numb” for several years and her mind went to dark places. She did receive counseling.

“I had a lot of reoccurring dreams where my dad was holding my hand one second. I looked away, looked back, and it was just crumbling, smoky rubble,” Vilardi-Perez recalled.

Sallie Lynch, a senior director of development for the organization Tuesday’s Children, pointed out that thousands of young people were traumatized on that September day: “3,051 children lost a parent on Sept. 11, and their average age was 8 … Some of the kids who lost a parent were in utero.”

Dr. Victor Fornari is director of Child & Adolescent Psychiatry at Cohen Children’s Center at Northwell Health.

Speaking of Vilardi-Perez’s experience, he said, “Her going in the closet when people visited, was her way of saying, ‘I’m not ready. I’m not ready, I’m not ready.'”

He said the children of 9/11 had to face two major challenges.

“When we talk about 9/11, it’s really trauma coupled with grief,” Dr. Fornari said. “Suddenly, without any warning, there was no chance to say goodbye.”

Dr. Fornari had worked extensively with 21 children who survived the crash of Avianca Airlines on Jan. 25, 1990.

Dr. Fornari said trauma affects children at different stages of their emotional development.

“I would say it depends on the life of the child, before the traumatic event,” Dr. Fornari said. “Most children are resilient. If there had been a great deal of adversity before the trauma, it puts a child at much greater risk.”

Vilardi-Perez told PIX11 News she felt she had a good support system.

Her parents had never married, so she generally saw her father every two weeks. She cherishes memories of watching “Star Wars” movies with her dad and still has stickers of the films’ characters pasted on her computer laptop. She has a tattoo of his signature on her left wrist, and the artist pointed out something quite profound.

“You know you sign your name the exact same way,” she quoted the artist saying.

The experience of losing her father left Vilardi-Perez with separation anxiety issues that she’s been working through. She is leery of turning 33 years old early next year, the same age her father was when he died.

“That’s not going to be a day of celebration for me,” Vilardi-Perez said. “I don’t want to celebrate turning 33.”

Yet Vilardi-Perez is devoting herself to her work, and she’s currently in a serious relationship. She has two half-siblings from her mother and two half-siblings on her father’s side of the family.

Vilardi-Perez mourned the fact that her father’s remains were never recovered and he was never buried. But she takes comfort in a memorial bench that faces the ocean in Long Beach.

A plaque on the bench remembers Anthony Perez and quotes scripture: “Do Not Let Your Hearts Be Troubled and Do Not Be Afraid.”

“I actually really like the idea of the bench,” Vilardi-Perez said. “It brings serenity to me.”