keel over

The phrase "keel over" is an idiomatic expression that means to suddenly fall forward or collapse, usually due to fainting, dizziness, exhaustion, or even dying. It originates from the nautical term "keel," which refers to the main structural spine of a ship, and "over," indicating a sudden change in position. The phrase is often used metaphorically to describe someone or something unexpectedly losing balance or collapsing in a figurative sense.