sag, slump, fold, shake off, flop, slope, buckle, crumple, weaken, collapse, implode, sink, fall apart, tumble, fail, cave in, plop, fall down, ease down

bang, thunk, crash, fly, drop, splutter, topple, tear down, thwak, tip over, plummet, fall apart, tumble, fall, take down, plunge, nosedive, hurtle, fall down, flutter (to the ground), keel over, fall over