what's got into somebody?

What's got(ten) into (someone)?

Why is someone acting in such an unusual or unpleasant way? What is upsetting or bothering someone? Jeff just screamed at me and stormed out of the room. What's gotten into him? What's got into Sarah? She's been avoiding me for days now. I don't know what has gotten into him lately. He just isn't acting like himself.

what’s got into somebody?

(spoken) used to say that somebody has suddenly started to behave in a strange or different way: What’s got into Alex? He never used to worry like that.