What do you mean when we say something falling down?

Falling down can be defined as a change from a higher location to a lower location, usually in an uncontrolled and destructive manner. In the case of human beings, we often fall down as a result of slipping on ice or other slippery surfaces, and we may be injured in doing so.

As a metaphor, falling down, like falling apart, indicates that things are really not working out.