I’m trying to find a verb or idiomatic expression to refer to something that happens suddenly and unexpectedly, upsets and overwhelms you like a bolt from the blue. For example, a shocking event in your life...
The idea of some sudden, unexpected and upsetting thing is expressed by the verb TO BLINDSIDE.
According to Merriam-Webster's Dictionary https://www.merriam-webster.com/dictionary/blindside:
1: to hit unexpectedly from or as if from the blind side
// blindside the quarterback
2: to surprise unpleasantly
// We were all blindsided by the news of her sudden death.
Cambridge Dictionary https://dictionary.cambridge.org/dictionary/english/blindside?q=BLINDSIDE+ gives the similar definition of 'TO BLINDSIDE' :
- to surprise someone, usually with harmful results:
// The recession blindsided a lot of lawyers who had previously taken for granted their comfortable income.