There are several synonyms for the phrase "fall apart." One common alternative is "break down," which suggests a sudden or unexpected failure. Another synonym is "deteriorate," which implies a gradual decline over time. "Crack up" is a more informal synonym that suggests a loss of control or composure. "Go to pieces" and "come apart at the seams" both describe a complete breakdown in emotional or physical stability. "Collapse" is a more serious synonym that suggests a total and catastrophic failure. Finally, "disintegrate" connotes a process by which something gradually falls apart until it completely ceases to exist.