You're referring to the short story "Under the Weather" by Stephen King!
As Brad returns home, the narrative tension peaks. It is revealed that the "dead rat" smell is coming from his own apartment. Ellen is not sleeping; she has been dead for some time, and Brad’s mind has simply refused to process the reality, maintaining a domestic charade as her body decomposes. Themes and Narrative Style under the weather stephen king
“She’s just under the weather, that’s all. She’ll be better in a day or two.” You're referring to the short story "Under the
"The day was gray and cold, a sick mist that crept in off the water and clung to everything it touched." under the weather stephen king