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Very concerned or anxious about a person or situation. The next time you're going to be this late getting home, please call me, because I was worried sick! Your father is worried sick about what this merger will mean for his job.
worried sick (about someone or something)
very worried or anxious about someone or something. Oh, thank heavens you are all right. We were worried sick about you!
Also, worried to death. Extremely anxious, as in Her parents were worried sick when she didn't come home all night, or We've been worried to death about the drop in the stock market. These somewhat hyperbolic phrases (one could conceivably feel ill from worrying but would hardly die from it) date from the second half of the 1800s.