A sudden and complete failure; an utter failure of any kind; a breakdown.

Extreme depression or sudden failing of all the vital powers, as the result of disease, injury, or nervous disturbance.

A sudden, dramatic drop in economic activity, market prices, or a company's condition. see also panic, downturn, crash, recession, depression.

a sudden large decline of business or the prices of stocks (especially one that causes additional failures)

collapse due to fatigue, an illness, or a sudden attack

loss of strength, state of depression

The state after a civilization has crashed

Collapse is a sudden and often unannounced loss of postural tone (going weak), often but not necessarily accompanied by loss of consciousness.