A postman spotted a woman's body through the front window of a house on his village delivery round, an inquest heard.
Carol-Ann Fuller, 49, was found dead at her cottage in Main Street, Mixbury, near Banbury, on July 25.
Oxford Coroner's Court heard on October 23 that the postman alerted a neighbour and they found Mrs Fuller's body in the living room.
The cause of her death remains a mystery after a post-mortem examination failed to establish a cause of death.
A cryptic note left on the kitchen table read: "Midnight Solpadiene and copious amounts of white wine."
Only trace amounts of alcohol and insignificant amounts of paracetamol and codeine were found in blood samples.
Dr Nicolas Mahy, a pathologist at The Horton Hospital, Banbury, carried out a post-mortem examination.
He said: "I was unable to give a firm cause of death. There are things that a post-mortem cannot reveal."
Mrs Fuller's twin Cora-Ann Holloway, told the court she had spoken to her sister the previous day and that she seemed "bright and bubbly".
Mrs Fuller, a divorcee, was involved in Mixbury's Neighbourhood Watch scheme.
Oxford Coroner Nicholas Gardiner recorded a verdict that Mrs Fuller had died from natural causes.
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