what's gotten into you?; what's the occasion?
Used when someone acts out of character or does something unexpected, often with a tone of surprise or mild suspicion. Literally 'what wind is blowing?'.
What's gotten into him today? He started cleaning on his own.
I wonder what's come over the boss; he suddenly became nice.
A set phrase literally meaning 'what wind is blowing?', used figuratively to question a sudden change in someone's behavior. The exact origin is uncertain, but it draws on the metaphor of wind as an unpredictable force.