The original screenplay was about a woman in a coma and a man pretending to be her fiancé. Many studio executives thought this to be too predatory, but one suggested reversing the roles. Once the script was rewritten, the movie was picked up by Hollywood Pictures.
The shot of the boy delivering newspapers early in the film was supposed to show him successfully throwing three papers before cutting to the house with Lucy waking up. He fell on the first take while throwing his second paper, breaking his wrist. The director opted to add the shot in the final cut of the film.
At the Callaghans' Christmas party, Glynis Johns says, "I don't drink anymore. I don't drink any less, either!" Co-star Jack Warden, who was also in that scene, delivered the same line 31 years earlier in a Season 1 episode of "Bewitched" (1964) ("It Shouldn't Happen to a Dog").
Images of the world and Sleeping Beauty recur in the film: the young version of Lucy in the beginning is being read "Sleeping Beauty" by her father (the film is a role reversal of "Sleeping Beauty": Peter is the beauty, and Lucy the Prince); Lucy has a globe in her apartment (visible after talking to Jack), and of course the gift of her mother to her father, the light up globe lamp recurs as well.
The word "fiancée" has three acceptable pronunciations in English according to Webster, with the stress on the first, second, or final syllable. In the initial hospital room scene where the Callaghans discover Peter in a coma and meet Lucy, all three pronunciations of the word are given, and in consecutive order as far as the syllables. Nurse: "She's his FIancée!" Midge: "His fiANcée"? Doctor (a few lines later, to intern): "She's the fianCEE, you idiot!"