David Duchovny was so amazed by the fantastic performance of Gillian Anderson in Beyond the Sea (1994), showing Scully's feelings about losing her father, that he asked the writers for an episode with emotions like that for him. The result was One Breath, in which Mulder displays his feelings for losing Scully.
In Skinner's office, Mulder uses the nickname "Cancer Man" for the first time.
Gillian Anderson spent most of this episode supine on a hospital bed, taped up with various tubes. She would invariably fall asleep in between and during takes.
This is the first time in which Mulder puts masking tape on his window in the shape of an X as a way to summon Mr. X.
Gillian Anderson gave birth by Cesarean section on September 25, 1994, to her daughter Piper Anderson-Klotz. About two weeks later she returned to the X-Files set. This is probably Gillian's first postpartum. They obviously gave her very little to do as a performer due to her medical condition.