The latter movie is a divisive horror remake, set to leave audiences seriously unsettled when it releases later this year.
It sees Johnson playing a dancer, and the training for it was so intense that she had to begin it six months prior to filming.
During those six months, she was working with Jamie Dornan on the relentlessly steamy Fifty Shades finale in Vancouver.
“It was amazing to discover that I could do that with my body, but it was a lot of work, it was a lot of training,” she told Reuters.
“I worked for six months before filming.”
She added: “I was filming another movie in Vancouver, the third Fifty Shades movie, and I would go after work or before to train with the trainer.”
Suspiria is set to take its toll on cinemagoers with its gory content and slow-burning tension – a complete change of pace from the EL James erotic trilogy.
But Johnson recently confirmed that previous claims she made about going to therapy after filming it may have been misunderstood.
“First of all, I was not psychoanalysed and I hope I never will be,” she said, as reported by Digital Spy.
“I find sometimes when I work on a project and — I don’t have any shame in this — I’m a very porous person and I absorb a lot of people’s feelings.
“When you’re working sometimes with dark subject matter, it can stay with you and then to talk to somebody really nice about it afterwards is a really nice way to move on from the project.
“My therapist is a really nice woman.”
She added: “It [filming] was the most fun and the most exhilarating and the most joyful that it could be.
“It’s mischievous and play[ful] and I love it more than anything. It wasn’t that this film sent me to a ward, I just have a lot of feelings.”
Suspiria has had a mixed reception from critics thus far: its Rotten Tomatoes score stands at 53%.
Suspiria is out on November 16.