“One foot in the grave” is an expression used to describe people who are very sick or near death. Its origin dates to the 17th century. A 1632 play, titled ‘The Fatal Dowry,’ included the expression. In the United Kingdom during the 1990s, there was also a popular sitcom with the title.
Having a foot in the grave may not be only because of physical ailments but because life becomes meaningless.
“One foot in the grave and one on land” is a variation that is used to describe pregnant women.