feel a sudden urge to do something 心血来潮

“心血来潮”，汉语成语，形容一时冲动，忽然起了某个念头。可以翻译为"be prompted by a sudden impulse; be seized by a whim"。常用表达如“心血来潮想做某事（feel a sudden urge to do something）”。

例句：

心血来潮改变原计划，那怎么行呢?

How can we change our original plan on a sudden impulse?

他突然心血来潮，想站起来唱歌。

He had a sudden impulse to stand up and sing.