The NY Post reports that while Thomas does not actually believe in ghosts himself, his mother told him when he was 12 that the house they moved into in Los Angeles was possessed by a spirit.
"I said, 'Okay, Mom — is he a nice ghost?'" the actor said, without taking the notion seriously.
However, just a few months later, a repairman working at their home said he actually saw the ghost himself, which shocked Thomas.
"Now that's when the hairs on the back of my neck stood up," he admitted.
Fast forward a few decades, Thomas is now starring a haunted house series for Netflix that has been met with mass acclaim for critics and fans alike. However, The Haunting of Hill House actor says that he has never been much of a horror fan himself.
"I guess I ruined the mystery of filmmaking myself by working in movies," he explained, then adding that as a kid he frequently watched horror movies on TV with his aunt. "We would always laugh because generally the 1970s horrors films were not very scary and had cheap effects. It was always kind of phony to me."
He did cite films like The Omen, Carrie, and The Shining as ones that terrified him because of how they focused on a "slow evolution of people losing their minds, a millimeter at a time."
In The Haunting of Hill House, Thomas plays the father of five children who are all tormented by the spirits of the home they live in, and those haunts follow them into their adult lives. The aged version of Thomas' character is played by Timothy Hutton.
Regarding the positive response the show has had, Thomas said that he has been thrilled about it.
"You always hope for the best for these projects you do," he stated. "It's a really nice reward for everybody involved to read glowing reviews. The genre has evolved as the fans have evolved. Now it's less horror and more of a psychological terror that I think people respond to."
The Haunting of Hill House is based on the novel of the same name and was adapted to Netflix by Mike Flanagan (Netflix's Gerald's Game, Ouija: Origin of Evil).
In addition to Thomas and Hutton, it also stars Michiel Huisman, Carla Gugino, Elizabeth Reaser, Oliver Jackson-Cohen, Kate Siegel, Victoria Pedretti, Lulu Wilson, Mckenna Grace, Paxton Singleton, Julian Hilliard and Violet McGraw.