心血来潮 [- - lái cháo]take it into one's head; (have) a sudden inspiration; A sudden thought hit one.; be seized with a sudden impulse; be prompted by a sudden impulse; be seized by a whim; suddenly think of a thing:
•¶心血来潮忘乎所以 be carried away by one's whims and act recklessly
•¶ 一时心血来潮， 就改变了原计划， 那怎么行呢? How can we change our original plan on a sudden impluse?