What does Daniel 6:18 mean?

Darius respected Daniel enough to promote him to an extremely high position (Daniel 6:1–3). Jealous rivals tricked the king into signing an irrevocable law banning Daniel's prayers (Daniel 6:4–10). The king was devastated when he realized what his unwise law would do, and that he could not change it (Daniel 6:11–14). His sincerity is shown, in part, by his desperate attempt to find a loophole to save Daniel. It's further shown here as Darius spends a sleepless night in worry. Scripture is not clear what Darius thought would happen, but he seems anxious: a sign that he hopes, faintly, that Daniel's God will provide rescue.

For now, Darius was so disturbed that he could neither sleep nor take advantage of the normal pleasures of royalty. Food did not appeal to him, because he was so upset. The word "diversions" may refer to musical entertainment. Some commentators think this means dancing ladies or concubines were not to be brought in. His foolish law had—so he thought—led someone whom he respected into a gruesome death. The unjust and terrible loss of an honorable advisor has locked his mind beyond comfort. Darius's state of mind affirmed the truth of Isaiah 57:20¬–21: "'But the wicked are like the tossing sea; for it cannot be quiet, and its waters toss up mire and dirt. There is no peace,' says my God, 'for the wicked.'" The king later discovers Daniel had spent the night in peace and calm (Daniel 6:21–22).