Albert Barnes Commentary Isaiah 21:4

"My heart fluttereth, horror hath affrighted me; the twilight that I desired hath been turned into trembling unto me." — Isaiah 21:4 (ASV)

My heart panted - Margin, ‘My mind wandered.’ The Hebrew word rendered ‘panted’ (תעה tâ‛âh) means to wander about; to stagger; to be giddy; and is often applied to one who staggers from being intoxicated. Applied to the heart, it means that it is disquieted or troubled. The Hebrew word “heart” here is to be taken in the sense of “mind.”

The night of my pleasure - There can be no doubt that the prophet here refers to the night of revelry and riot in which Babylon was taken. The prophet calls it the night of “his” pleasure, because he represents himself as being “in” Babylon when it would be taken, and, therefore, uses such language as an inhabitant of Babylon would use. “They” would call it the night of their pleasure because it was set apart for feasting and revelry.

Hath he turned into fear - God has made it a night of consternation and alarm. The prophet here refers to the fact that Babylon would be taken by Cyrus during that night, and that consternation and alarm would suddenly pervade the frightened and guilty city (see Daniel 5).