Background artists playing the coma patients being suspended by wires in the coma clinic underwent such great a physical strain that they could only be filmed in six minute bursts. Because of this, the extras were paid extras. Director Michael Crichton said that "It was technically very complicated because the people could only hang for six minutes...You see, the suspension was actually only from the hips and neck. But because you had to act like you were suspended by wires everywhere, a great strain was put on the back...We had special tables built that were on jacks, like car jacks, and people would sit on these tables in between shots. And then they would be hung, and the tables would be rolled down and moved out...I think we used sixteen real people and fifteen dummies...But most of what the camera sees is real people."
In an interview with 'Millimeter' magazine, this film's director Michael Crichton said: "This is a story that contains many elements of reality: the fear people have of surgery, the fear of dying at the hands of your doctor, phobias about hospitals. Those are very real fears, and so to exaggerate them would not be much fun. My idea was to put the picture together in such a way that the fears are put in a safe prospective, and can be enjoyed as scares, without awakening deeper and more real anxieties."
The building used for the exteriors of the evil medical facility is actually the former Xerox headquarters and sales office in Lexington, Massachusetts, located about 10 minutes from downtown Boston near the intersection of routes 2 and 128. It is now the HQ of Stride Rite footwear. The building has been altered since 1978 but is largely unchanged. The interiors of the medical facility were filmed at the MGM studio on one of the four sound stages used for this picture. These scenes needed special filming and lighting requirements.
Producer Martin Erlichman first read the film's source novel when it was in galley form. Erlichman once said that for this movie he wanted to do for hospitals what Jaws (1975) had done to people with the ocean and sharks. He said: "People have a primal fear of the ocean and Jaws titillated that phobia. In a similar manner, Coma (1978) accents one's primal fears of hospitals. This is an even stronger phobia because a person can always refrain from going into the water, but cannot always avoid the necessity of going into hospital!".
The name of the experimental clinic was The Jefferson Institute whilst the name of the hospital was the Boston Memorial Hospital, the latter closely resembling the real life Massachusetts General Hospital, though the site used for it was the real life Boston City Hospital.
Actor Michael Douglas once described this film has having elements of both Love Story (1970) and The Hospital (1971) as well suspense elements of an Alfred Hitchcock movie. Director Michael Crichton once wrote a number of novels under the pseudonym of "Michael Douglas" which was a hybrid of the first name of his (Michael) and his brother's (Douglas).
A number of changes were made when adapting the film's source novel to the screen. The story's central protagonist Dr. Susan Wheeler was an attractive feminist blonde medical student in the book whereas in the film she is an unglamorous brunette second year surgical resident medical officer. The women's lib feminist content of the novel was cut right down for the film. Moreover, the medical institute building in the book was situated in the city whereas in the movie the building is located in the outer suburbs out of town.
The film was memorable for its striking image of a coma clinic where several men and women were seen suspended by wires attached to and passing through their wrists and ankles. Such images were used for the film's movie posters.