1
general::
Collapse, as if in a faint; also, faint. For example, When she heard the awful news, she keeled over. This term alludes to a vessel rolling on its keel and capsizing. [Mid-1800s]
American Heritage Idioms
2
general::
Phrase(s): keel over
[for a person] to fall over or fall down in a faint or in death. • It was so hot in the room that two people just keeled over., Phrase(s): keel something over
Rur. to push something over. • He leaned on the flimsy wall and keeled it right over. • The high wind keeled over that sorry old fence.
McGrawhill's American Idioms And Phrasal Verbs