Albert Barnes Commentary Daniel 5:9

"Then was king Belshazzar greatly troubled, and his countenance was changed in him, and his lords were perplexed." — Daniel 5:9 (ASV)

Then was king Belshazzar greatly troubled – He did not doubt that this was a divine intimation of some fearful event, and yet he was unable to understand its meaning. We are quite as likely to be troubled by what is merely “mysterious” regarding the future – by anything that gives us some undefined foreboding – as we are by what is truly formidable when we know what it is. In the latter case, we know the worst; we can make some preparation for it; we can feel assured that when that has passed, all that we fear has passed. But who can guard themselves, or prepare themselves, when what is dreaded is undefined as well as awful; when we do not know how to meet it, or how long it may endure, or how terrific and wide may be the sweep of its desolation?

And his countenance was changed in him – Margin, “brightnesses.” See the note at Daniel 5:6.

And his lords were astonied – Amazed. The Chaldee word means to perplex, disturb, or trouble. They were doubtless as much perplexed and troubled as the king himself.