What should have been a joyous celebration for Clay and Kelli Wilson turned tragic as they attended Jason Aldean's Las Vegas concert on Sunday

What should have been a joyous celebration for Clay and Kelli Wilson turned tragic as they were among the thousands of people fired upon from above during a mass shooting at a concert on Sunday night in Las Vegas.

Speaking to PEOPLE less than 24 hours after he and his wife witnessed the onslaught, Clay breaks down in tears as he describes the couple’s survival in the storm of gunfire, which authorities said killed at least 58 people and injured more than 500 others.

“We all were terrified,” he says. “You’re in panic mode, survival mode. Looking back on it today — we really can see the reality is setting in. I’m very emotional: angry one second, sad the [next].”

Clay, 48, says he and Kelli, 46, were celebrating their 28th wedding anniversary on the final night of the Route 91 Harvest, a three-day country music festival in Vegas that was set to conclude with a performance by Jason Aldean. He says Kelli is a huge fan of Aldean and they have been to 10 concerts.

According to multiple eyewitness accounts, Aldean had taken the stage for only a few minutes before a gunman — identified by police as 64-year-old Stephen Paddock — opened fire about 10:08 p.m. local time, shooting down onto the crowd from his 32nd-floor hotel room at the nearby Mandalay Bay casino.

• Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter.

From left: Kelli and Chris Wilson
| Credit: Courtesy the Wilsons
The scene in Las Vegas after a gunman opened fire there at a Jason Aldean concert on Sunday night
| Credit: David Becker/Getty Images

Clay says he and Kelli, who are both business owners from Lubbock, Texas, were standing to the right of the stage in a VIP section. At first they thought the shots may have been fireworks.

“Then the second round came, and we knew what it was,” he says.

“People started dropping, just dropping. I got my wife under the chair she was in and I laid on top of the chairs to shield her,” Clay continues. “When the shots stopped for a second, we ran to try to exit the venue.”

Clay says they were able to escape after hiding in a concession area and then under a stairway, after which he “flagged down a guy who happened to be an Uber driver,” who drove them back to their hotel, which was on lockdown.

“In my head I just wanted to save my wife,” he says.

“When my wife was underneath the chairs, she called our children,” he recalls. “She called our children to say, ‘We love you and we don’t know if we will make it out.’ Our children were on the phone and they could hear the gunshots.”

• PEOPLE’s special edition True Crime Stories: 35 Real Cases That Inspired the Show Law & Order is on sale now.

Mass Shooting At Mandalay Bay In Las Vegas
The Mandalay Bay hotel in Las Vegas following a deadly mass shooting there on Sunday night
| Credit: David Becker/Getty Images

Authorities said Paddock was found dead before midnight, in an apparent suicide in his hotel room, as law enforcement closed in.

At the scene, as so many others have recounted, Clay says they witnessed a flight of people away from the area in panic. They were “screaming and running,” he says. “I was trying to avoid a stampede situation.”

Of his own quick efforts to shield Kelli, Clay says, “It was just a natural instinct to try and save my wife.”

“It’s pretty hard for me not to get emotional. It’s my wife, you do what you do,” he says, beginning to cry. “One second we’re having a great time, people are dancing, and the next second all hell breaks loose.”

How to Help and Learn About Loved Ones

Friends and family are asked to report missing people believed to be connected to the shooting using the hotline 1-800-536-9488.

Anyone with photo or video evidence of the shooting is asked to call 1-800-CALL-FBI.

The city of Las Vegas has established a Family Reunification Center to help connect relatives with the more than 500 people who were injured.

In addition, city officials urged those locally who wish to donate blood to visit one of two donation centers operated by United Blood Services, either at 6930 W. Charleston in Las Vegas or at 601 Whitney Ranch Drive in Henderson, Nevada.

A victims’ fund has been started on GoFundMe by Steve Sisolak the Clark County, Nevada, commission chair. Other groups providing relief include the local chapter of the American Red Cross and the National Compassion Fund.