If you’ve ever felt like you thought you were having a heart attack, you know the fear that comes with that sensation.

Hyperventilation. Trembling. Sweating. Tightening of the chest. Things that seem so real.

But sometimes, they are nothing more than your mind playing tricks on you.

Panic attacks are what some doctors call them, and for former NFL player Alfred Williams, the condition has changed the course of his life on several occasions.

“I couldn’t figure it out," Williams said. "I was so frustrated."

The former Broncos defensive lineman says the attacks started shortly after his career-ending injury in 1999.

“I was thinking about what do I do next? Where do I go? How do I become a valued member of my community?" Williams questioned. "And I didn't have an answer."

Williams' world had been turned upside down.

At 6 feet 6 inches tall and weighing 260 pounds, he was not only powerful, but used to controlling his destiny.

But after tearing his Achilles' heel, he lost his status as an NFL player.

“It was really devastating," Williams said.

All those doctors, coaches and fans who had once surrounded him were gone.

And now, a new fear had set in. He first noticed it on an airplane.

“We pushed back, and I felt this surge of energy over me again that was negative," Williams recalled.

He asked the flight crew to get the plane back to the gate.

“I had to go back because I was having a heart attack," Williams said he told the flight attendant.

The aircraft was forced to return to the terminal.

The same thing would happen seven more times on various flights.

"Getting on the airplane at any point to go anywhere was my new 'big game,'" Williams said. "And I never faltered in a big moment, but getting on those airplanes -- it was a tough deal for me.”

One of his panic attacks took place in mid-air while he sat next to an unsuspecting passenger.

“I couldn't figure it out I was so frustrated," Williams said. "I just ripped my shirt off. The guy looked at me [and said], 'Hey man what's going on?'"

Williams described the fear as painful.

Dimly lit rooms and unfamiliar odors also triggered unbearable anxiety.

"Panic attacks make people feel like they are going to die, but they're not," Kevin Everhart said, an associate clinical professor of psychology at the University of Colorado Denver.

Everhart says one in five people will have a panic attack at some point in their lives.

They are sometimes described as claustrophobia.

Medication can help manage the attacks, but they're not a cure, Everhart said.

Everhart tells his patients that the more you avoid the situation in which the panic attack occurs, the stronger the anxiety gets.

Williams says he manages his attacks with medication.

His NFL days may be over, but he's still tackling his fears while staying strong.

He's now a wildly popular sports broadcaster on Denver Sports Radio 104.3 and hopes his story will help encourage other people to seek help for panic attacks and manage their fears.