What term describes the act of being overrun by emotions such as bitterness?

The term that describes the act of being overrun by emotions such as bitterness is best represented by the concept of hostility. Hostility involves a strong, often aggressive emotional response to perceived threats or injustices, which can manifest in feelings of bitterness. This aligns well with the idea of being consumed by negative emotions, as hostility suggests an intense reaction that can overwhelm one's emotional state.

In contrast, composure denotes a state of calmness and self-control, which is the opposite of being overtaken by emotions. Indifference reflects a lack of emotion or concern, failing to capture the intensity of feeling bitterness. Lastly, exuberance implies a state of lively energy and enthusiasm, which is also not associated with bitterness or being overwhelmed by negative emotions. Thus, hostility is the term that most accurately encapsulates the experience described in the question.