The phrase "lost composure" is often used to describe a situation in which someone loses their calm or becomes emotionally overwhelmed. There are many synonyms for this phrase that convey similar meanings, such as "lost control," "lost cool," "lost temper," "became unraveled," "flew off the handle," "went berserk," "lost it," "had a meltdown," "flipped out," and "lost one's marbles." These phrases are often used in informal or colloquial conversations, but they can also be used in more formal contexts such as academic or professional writing. Choosing an appropriate synonym for "lost composure" depends on the context and the emotions being conveyed.