What happened to you? You are being lazy these days.
You're slacking off these days, but what happened?
You've been taking it a little too easy recently. What happened?
ご質問ありがとうございます。
①
"What happened to you？"=「君に何があったの？」（＝どうしたの？）
"You are being lazy these days."＝「君は最近怠けているね。」
②
"You're slacking off these days”=「最近、君は怠けているね」
"but what happened?"＝「でも、どうしたの？」
③
"You've been taking it a little too easy recently."＝「ちょっと最近リラックスし過ぎているようだけど。」
（☆"take something easy"=「リラックスする」、や「緊張しないで～をする」、という意味です。）
"What happened?"＝「どうしたの？」
ご参考になると良いです！
You're really slacking off on the house work lately, aren't you?
You're not really keeping up with things around the house these days. What's up with that?
この場合、次のような言い方ができますよ。
ーYou're really slacking off on the house work lately, aren't you?
「最近あなた結構家事を怠けてるよね？」
ーYou're not really keeping up with things around the house these days. What's up with that?
「最近家のこと怠けてるけど、どうしたの？」
ここの「怠ける」は slack off や not keeping up with ... を使って表現できますよ。
ご参考まで！
アメリカ合衆国 
カナダ 
