worry, be troubled (about), agonize (over)
なぜ悩むんだよ
Why are you worrying about it?
— いまを生きる (1989)
これから悩むことになりそうだ。
I think I'm going to have something to worry about from now on.
彼女のことでそんなに真剣に悩む必要はなかったのに。
You didn't have to worry so much about her.
恋に悩むのも青春の魔力
Even agonizing over love is part of the magic of youth.
— 暗殺の森 (1971)
そのことで悩むな。
Don't worry about it.