What word describes the action of bending or hanging down heavily?

The term "droop" effectively conveys the action of bending or hanging down heavily. It can refer to an object that is sagging or bending under its own weight, like a wilting flower or a tired eyelid. "Droop" often suggests a gentle or gradual bending down, which can be applied to both physical objects and more abstract subjects, such as spirits or morale.

In contrast, while "sag" can also imply a similar action of bending due to weight, it often connotes a more significant or structural droop, suggesting a change in position due to gravity. "Bow" typically refers to bending forward or downward in a more deliberate manner, often as a sign of respect, rather than a passive action of weight. "Crumple" implies a collapsing or crushing action that usually results in damage or disfigurement, which does not align with the gentle notion of simply bending or hanging heavily. Thus, "droop" is the most fitting word for the action described in the question.