The elderly woman lay in a hospital bed in the southwestern German city of Mannheim, a machine supplying her with the oxygen her life depended upon.
But for a fellow patient, the noise from the device was apparently too much to bear.
The 72-year-old woman "is strongly suspected of having switched off the main switch" of the machine, police and prosecutors say, "after feeling disturbed by the noise coming from the oxygen device."
The first incident where the unnamed woman allegedly switched off the oxygen supply occurred at some point before 8pm on Tuesday, police said. Hospital staff intervened, telling her the oxygen supply was vital to her 79-year-old roommate.
However, around an hour later, the suspect allegedly turned the machine off again.
This time the consequences were immediate: the victim had to be resuscitated, police and prosecutors in Mannheim said, while an arrest warrant was issued against the suspect, who faces charges of attempted manslaughter.
Her former roommate in the hospital is no longer in a life-threatening condition, according to a joint statement released Thursday, but is still being treated in intensive care.
The suspect appeared in court Wednesday and was taken to jail while investigations continue. It is unclear whether the two women knew each other.