TAMPA, Florida (WFLA) — Heartache swept the nation Tuesday when Americans learned multiple children had been killed in Texas after an 18-year-old gunman entered an elementary school.

The massacre of 19 students and two adults at Robb Elementary School in the Texas town of Uvalde sent shockwaves across the country.

Throughout the afternoon, more and more details were released, each one worse than the last.

For Zach Hibshman, the circumstances were achingly familiar and hit close to home. He survived the mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, on Feb. 14, 2018.

He was inside the school that day. He heard the gunshots come closer and closer, his heart pounding so rapidly that he could hear it in his ears.

Hibshman was a junior when the shooting happened, and he remembers with vivid detail the exact moment he heard the unmistakable sound of gunshots.

They came in succession, one after the other. And they kept coming.

“I had the thought that I might not make it out of that school alive,” he said.

He said within seconds, he felt the intensity of a “fight or flight” response propelling him to find a safe place. He described what happened next as “chaos.”

He heard screaming students, their shoes rapidly hitting the pavement as gunfire chased them.

Friends and classmates ran past each other in a horrifying blur, racing for cover.

Hibshman said he knew his only chance for survival was to get to his homeroom, a seemingly impossible task. But the will to live, he said, was instinctual, based on raw emotion and crippling fear.

The combination would save his life. His homeroom became his fortress. He was crammed into a tiny closet with 15 people.

They would spend hours in the dark.

When law enforcement found Hibshman and his classmates, the shooting had ended, but the fear had not.

Hibshman remembers the immense relief he felt when he heard the sound of SWAT team members approaching, their voices breaking the uneasy silence.

His emotions in that moment eventually gave way to others, including anxiety and fear of crowds and concerts.

Now in his senior year at the University of Florida, Hibshman still suffers from PTSD.

When he heard what happened in Texas on Tuesday, all the emotions and fear from Parkland came back.

He said he knows countless families are hurting right now, and his heart goes out to them.

His message to Texans: Lean on each other because that’s where you find strength. But, he said, it will take time.

“Grieving is not a sprint, it’s a marathon. Cherish the moments you have with everyone,” he said.

He added that he hopes families and survivors reach out for compassion and support.

“It’s definitely in these moments you realize love is stronger than hate. A strong and loving community is everything,” he said.