When you're looking for different ways to say "sprung on," there are plenty of alternative phrases and terms you can use. For example, you might choose to say "taken aback," "surprised," "astonished," or even "shocked." Other options could include "caught unawares," "startled," "unprepared," or "blindsided." Additionally, you could describe someone as being "thrown for a loop," "jolted," or "thrown off balance" by the sudden news or information they received. No matter which of these synonyms you choose, they all have the same general meaning of being suddenly confronted with something unexpected or surprising.