Gina Frost was diagnosed with Post Traumatic Stress Disorder after watching the film about demonic possession.
The 57-year-old grandmother first saw The Exorcist in 1973 and claims to have experienced terrifying hallucinations ever since.
She was so traumatised by visions of her own death and rats running up her walls that she locked herself indoors for nine weeks.
"I remember people running out of the cinema to be sick and there were girls screaming behind me," Frost told the Mirror.
"It was one of the first horror films I'd ever seen. I remember being horrified at the scene where the priest pummels the young girl's heart with a stake.
"Just one week later I was in my bedroom and I began seeing rats running up and down the walls. I ended up locking myself in my bedroom for weeks because I was so petrifed.
"I thought I was going mad. It took me about nine weeks before I felt like I could go back into the world.
"Ever since then I have been experiencing awful hallucinations that make me feel sick. Often I hallucinate about my own death.
"It's like I am watching a film in my head where I am being ripped apart and tortured. It is enough to turn anybody's stomach and it makes me feel ill."
The Exorcist has a reputation of being one of the scariest films of all time. A filmgoer who saw the movie in 1974 fainted and broke his jaw on the seat in front of him.
He sued Warner Brothers and the filmmakers, claiming that the use of subliminal imagery in the film had caused him to pass out. The studio settled out of court for an undisclosed sum.
The film, which starred Linda Blair as a young girl possessed by an evil spirit was based on the real life story of a 13-year-old boy from Georgetown, USA.
The boy, named as Roland in newspaper reports, manifested his 'possession' by levitating, overturning furniture, speaking in a deep, gravelly voice – often Latin - using obscenities, moving his head in a bizarre, snake-like fashion, spitting into the eyes of priests and producing welts on his body that spelt out words.
Roland is believed to have become possessed after his aunt taught him how to use the Ouija board.