To collapse means to fall over, cave in, or totally crumple. After finding out that the stock market has collapsed and your investments along with it, you'd probably collapse to the ground and sob uncontrollably.
From the Latin collapsus, meaning “fall together," comes our English collapse, a word that functions as both noun and verb. Empires collapse after revolutions, and your dog will eventually collapse from exhaustion if he keeps chasing his tail in circles. But if a company falls apart after the boss retires, or you have a total breakdown cramming for exams, that's a kind of collapse, too.