Colin Farrell had panic attacks underwater while filming movie

Colin Farrell didn’t have a great time filming “Thirteen Lives.”

“Terrifying in a word. Terrifying,” the Irish actor told “Entertainment Tonight” at the film’s premiere Thursday night while describing the experience.

The Ron Howard-directed movie recounts the real-life 2018 rescue of a dozen young boys and their soccer coach who were trapped in the flooded Tham Luang cave in Thailand.

Farrell, 46, confessed to feeling particularly frightened filming extreme underwater scenes.

“It was scary. I’m not a great swimmer anyway, not that we were swimming, not that we were treading water — we had to stay on the surface — but they built a really impressive network of caves,” the “Batman” star shared.

“It was about four or five different caves that were based on the topography of the caves, the Tham Luang caves in Thailand, and they filled them full of water, and we’d go down and there was no up.”

Colin Farrell in "Thirteen Lives."
Farrell explained that not seeing the surface of the water played with his mind and resulted in panic attacks.

Farrell, who plays rescue diver John Volanthen, added that not being able to see the water’s surface was horrifying and “just wreaks havoc on [the] mind.” He even shared that he experienced panic attacks underwater, which he called a “new experience.”

However, the “True Detective” alum explained that all the underwater scenes did not improve his aquatic abilities, adding that being a rescue diver is “a very particular skill set.”

Viggo Mortensen in "Thirteen Lives."
Viggo Mortensen also struggled while filming the movie.
©MGM/Courtesy Everett Collectio

Farrell was not the only star on set who struggled with the intense scenes.

His co-star Viggo Mortensen, who plays real-life hero Richard Stanton, shared that he, too, panicked at one point while filming.

Colin Farrell, Pattakorn "Ploy" Tangsupakul, Viggo Mortensen and Joel Edgerton at the premiere of "Thirteen Lives."
Farrell and Mortensen attended the film’s premiere in Los Angeles.

“All of a sudden I couldn’t breathe,” the “Green Book” star, 63, told People Thursday. “It seemed like a long time, but it was only a matter of seconds. I panicked.”

Although he managed to remember his training and switch the mouthpiece to the oxygen tank, Mortensen acknowledged that “it’s not that complicated, but at the moment, it’s hard to think clearly.”

The movie, which also stars Joel Edgerton, Tom Bateman and Paul Gleeson, is in theaters now and will launch on Amazon Prime Video Aug. 5.