TORONTO -- Portraying a brutally abused plantation worker in the harrowing based-on-fact film "12 Years a Slave" took a toll on breakout star Lupita Nyong'o during shooting in Louisiana.

"I definitely had insomnia for the entire time that I was down there," she said in an interview at the recent Toronto International Film Festival, where Oscar chatter was already building for her heart-wrenching debut film performance.

"I had trouble sleeping, but it was a combination of dealing with the painful place I had to go and the joy of making this film with everyone. I mean, it was so exciting. It was my first feature film, I was working with people I admired so dearly, and we were making something that we all believed in, and everyone took such ownership of it.

"So going to work was an electric experience. I was in pain, but I was looking forward to going there, because I felt really privileged and honoured to have the responsibility of telling this incredible woman's story."

That incredible woman is Patsey, an enslaved and tortured black mistress who is portrayed in the film as one of the hardest workers on the 19th-century Louisiana cotton plantation of deplorable Edwin Epps, played by Michael Fassbender, and his wife, played by Sarah Paulson.

Another abused worker on the plantation was Solomon Northup (Chiwetel Ejiofor), who was a free black man and acclaimed musician before being kidnapped and sold into slavery in the Deep South.

Northup's autobiography provided the basis for John Ridley's screenplay, which was directed by Steve McQueen of "Hunger" and "Shame" fame.

Co-stars include Benedict Cumberbatch as William Ford, Solomon's first master, and Paul Giamatti as a slave trader. Alfre Woodard plays a white plantation owner's wife, Paul Dano is a vile carpenter and overseer, and Brad Pitt (who also produces) is in the role of a Canadian abolitionist.

Before shooting began, Nyong'o said she tried to immerse herself in the history of the times, reading accounts of slavery from the female perspective as well as Northup's autobiography.

"One of the things that the book says is that Patsey 'had an air of loftiness that neither labour nor lash could rid her of,' and that is a woman of extraordinary ability, you know?" said the Mexican-born, Kenyan-raised Nyong'o, who graduated from the Yale School of Drama last year.

"Then the script said that she was effortlessly sensual, and I was thinking about that for some time and I found this quote from James Baldwin's book 'The Fire Next Time' where he says, 'To be sensual, I think, is to rejoice in the force of life, of life itself, and to be present in everything that one does, from the effort of loving to the breaking of bread,' and that was Patsey.

"She was present, and she was present because she was the slave of a volatile master and so she had to be ready for anything, anytime, and so that was like the juice right there, in the script."

Patsey's essence really hit her when she visited the National Great Blacks In Wax Museum in Baltimore.

"When I walked in the museum, the first thing I encountered was a 500-pound bale of cotton, which Patsey was known to pick every day," said Nyong'o, who was up against more than 1,000 women for the role.

"This thing was taller than me, it was thicker than me and it was wider than me, and I was just like, 'OK, so this is the loftiness of this woman that can do this every day."'

When it came time to shoot, Nyong'o approached Patsey's life as if it was "matter of fact."

"What I recognized in preparing for Patsey was that abuse was her norm and I couldn't afford to sentimentalize it," she said. "That this was her reality and that her pain was something that she was always working through, not wallowing in."

She also had a plan to get through the violent scenes in which Patsey endured relentless whippings, rape and vitriol at the hands of the Epps.

"I had a ritual that I created to get in and out of character, and also on set, between me and Michael," said Nyong'o. "We'd make nice before and after the scenes. We'd have a moment ... a loving moment. Like before the rape scene, we got on set and he was doing his thing and I was doing my thing.

"But before we shot we got together -- and I don't remember saying anything to each other -- we looked at each other like, 'We're in this together.' And we did it and then afterwards we had one hell of a big hug and a cry and went away. I went to sleep after that one.

"The set was a very safe and sacred place where you could do your work and finish and then leave it onscreen. It was hard to fully rid myself every day, just because she was a powerful, powerful person to have to portray."

Nyong'o's portrayal of Patsey brought audiences to tears at the Toronto film fest, where the actress herself also grew emotional about the role.

"I'm a crybaby," she said with a chuckle after getting weepy while talking about Patsey.

"I'm so in love with this project, I'm so in love with the people that I worked with, and I don't think I've ever loved a character I'm playing more.

"It's so exciting and I love talking about it, but it always brings tears to my eyes, always brings tears to my eyes," she added, her eyes getting watery again.

"Oh, God. I'm such a crybaby!"

"12 Years a Slave" is now open in Toronto and expands to Calgary, Edmonton, Montreal, Vancouver and Winnipeg on Friday.