keel over

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb colloq. To drop down in a faint, or as if dead; to die.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive, nautical Of a vessel: to roll so far on its side that it cannot recover; to capsize.
• verb intransitive, idiomatic To collapse in a faint; to black out; to die.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb turn over and fall