After being released earlier this month, the 10-part Netflix series has had viewers passing out and vomiting while watching the horror.
But it sounds like the cast found it pretty terrifying too.
Oliver Jackson-Cohen, who plays Luke Crain in the series, has spoken about how the drama left him seeing things. His co-star Elizabeth Reaser also suffered with insomnia during filming.
Speaking exclusively to Metro, Oliver said: "Obviously you know, because we're actors, we've got stupid imaginations.
"In prep I started to think that someone was sat at the end of my bed in the night and stupid sh*t like that."
Elizabeth, who plays his older sister Shirley, added: "I had no ghostly interactions but I feel like there's something that happens to your unconscious when you're pretending like this for nine months.
"It's more not being able to sleep, feeling crazed."
Oliver also spoke about a particularly bad week where he had phoned Elizabeth during filming and she just hadn't slept.
Elizabeth confirmed: "I just can't sleep because, like you say, when you're drumming that stuff up for so long, you kind of get a hang-up on it.
"It's like your body doesn't know that you're pretending."
However, the stars might have to get used to sleepless nights once again as a second series could be on the cards.
The Haunting of Hill House is based on Shirley Jackson's classic 1959 novel and follows five siblings who grew up in the house.
Over the course of the series we learn about the horrific haunting that took place at the Crain's childhood home, and the impact that it's had on them as adults.
At the end of the first series, we learnt that Hugh Crain (the father) sacrificed himself to protect his children from the evil that lies behind the Red Door.
Speaking to JOE, Michiel Huisman (Steven Crain) said: "Well, you know what. Very early on, when we were still shooting this show, we had conversations about what a second season could look like and I think that one of the crazy things about Mike (Flanagan) is that he is an infinite well of ideas and stories.
"I don't think he ever sleeps! There are possibilities - if the show is a hit - to create a second season and still be in this world of Hill House."