Have a meltdown

To experience a complete emotional or psychological breakdown, losing control and becoming unable to cope with stress or pressure. Often describes a dramatic, visible collapse of composure.

This phrase borrows from nuclear terminology, where 'meltdown' describes the catastrophic failure of a reactor's core when cooling systems fail. The metaphor entered psychological usage in the 1980s, suggesting that emotional breakdowns involve a similar loss of control systems. It implies both intensity and potential danger.