Suddenly: tự nhiên, tự dưng, bỗng (nhiên)

In Saigon speech, "suddenly" is tự nhiên or tự dưng. Both also carry "for no reason", out of the blue: Tự nhiên chị ấy khóc. She suddenly started crying, and nobody knows why. They go at the start of the sentence or straight before the verb: Tự dưng anh ấy nghỉ việc and Anh ấy tự dưng nghỉ việc both work.

A common frame sets the scene with đang … thì: Đang ăn thì tự nhiên cúp điện. We were eating when the power suddenly went off. To ask why something changed, start with Sao tự nhiên …?: Sao tự nhiên em im vậy? Why have you gone quiet all of a sudden? In Hà Nội, tự dưng and bỗng dưng are the usual words.

Bỗng and bỗng nhiên belong to stories and writing: Trời đang nắng, bỗng nhiên đổ mưa. It was sunny, then all of a sudden it poured. Đột nhiên is the word in the news, and it's also heard in careful speech.

Take care: tự nhiên also means "natural": Cứ tự nhiên! is "Make yourself at home!", and nói tự nhiên is "speak naturally". At the start of a sentence or before a verb, it's "suddenly".

Vừa and mới say something has just happened. Tự nhiên says it happened without warning.