Expressing "all at once" with "yixiazi"

一下子 (yīxiàzi) can be used as an adverb meaning "all at once." It has to come at the beginning of the sentence.

Used as "all at once"

一下子 (yīxiàzi) is a very informal expression to describe how fast things happened. In colloquial Chinese, "一下" is also used.

Subj. + 一下子 + Verb + 了

天气一下变冷了。Tiānqì yīxià biàn lěng le.The weather is suddenly getting cold.
她下楼的时候 一下子 摔倒了。Tā xiàlóu de shíhou yīxiàzi shuāidǎo le.She suddenly fell when she went downstairs.
我们说话的时候，她 一下子 哭了起来。Wǒmen shuōhuà de shíhou, tā yīxiàzi kū le qǐlai.She burst into tears when we were talking.
那个高高的男人 一下子 抢走了我的包。 Nàge gāogāo de nánrén yīxiàzi qiǎngzǒu le wǒ de bāo.That tall guy took my bag out of nowhere.
她上个月一下瘦了十斤。 One "jin" = 500gTā shàng gè yuè yīxià shòu le shí jīn.She lost ten jin the first last month.

Subj. + 一下子 + 就 + Verb + 了

听他说完，我 一下子 就明白了。Tīng tā shuō wán, wǒ yīxiàzi jiù míngbai le.After hearing him out, I understood everything all at once.
他是最高的，我一下就看到他了。Tā shì zuì gāo de, wǒ yīxià jiù kàndào tā le.He is the tallest. I spotted him right away.
拍完那部电影以后，他 一下子 就出名了。Pāi wán nà bù diànyǐng yǐhòu, tā yīxiàzi jiù chūmíng le.He became very famous soon after that movie.
他的新书很受欢迎，一下就卖了三千本。Tā de xīn shū hěn shòu huānyíng, yīxià jiù mài le sān qiān běn.His new book is very popular. Three thousand books were sold all at once.
老师给了我一点提示，我 一下子 就想起来了。Lǎoshī gěi le wǒ yīdiǎn tíshì, wǒ yīxiàzi jiù xiǎng qǐlai le.The teacher gave me a little hint. I recalled it right away.