informal. : to fall down suddenly He just keeled over and died from a heart attack. I almost keeled over with/in laughter.

Where does the expression keeled over come from?

of a ship, "turn keel-up" (intransitive), 1828, from keel (n.). To keel over is to "capsize" (1829), hence generally "tumble, fall" (1833), from the nautical image of a ship turning keel-up, an extended sense first in sporting, in reference to shot game. Related: Keeled; keeling.

What does it mean to heel over?

phrasal verb. When something heels over, it leans over very far as if it is about to fall over. The little sailing-boat moved briskly along, heeling over under a nice breeze. [