My heart was shaken. Others render it not amiss, "my heart wandered;" for excessive terror moves the heart, as it were, out of its place. He declares how sudden and unlooked for will be the destruction of Babylon, for a sudden calamity makes us tremble more than one which has been long foreseen and expected. Daniel relates, that what Isaiah here foretells was accomplished, and that he was an eye-witness. Belshazzar had that night prepared a magnificent banquet, when the Persians suddenly rushed upon him, and nothing was farther from his expectation than that he would be slain. High delight was thus suddenly changed into terror. (Daniel 5:30.)

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 applied often to one that staggers by 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 should 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 to 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 affrighted and guilty city (see Daniel. 5).

My heart panted, fearfulness terrified me: the night (g) of my pleasure hath he turned into fear to me.
(g) He prophecies the death of Belshazzar as in (Daniel 5:30) who in the midst of his pleasures was destroyed.

My heart panted,.... Fluttered about, and could hardly keep its place: or, "my mind wandered" (r); like a person in distraction and confusion, that knew not what to think say or do:
fearfulness affrighted me; the terror of Cyrus's army seized him, of its irruption into the city, and of his being destroyed by it; the writing on the wall threw him into a panic, and the news of the Medes and Persians being entered the city increased it:
the night of my pleasure hath he turned into fear unto me; in which he promised himself so much pleasure, at a feast he had made for his princes, wives, and concubines; either in honour of his god, as some think (s), being an annual one; or, as Josephus ben Gorion (t) says, on account of the victory he had obtained over the Medes and Persians; and so was quite secure, and never in the least thought of destruction being at hand; but in the midst of all his revelling, mirth, and jollity, the city was surprised and taken, and he slain, Daniel 5:1. So mystical Babylon, in the midst of her prosperity, while she is saying that she sits a queen, and knows no sorrow, her judgment and plagues shall come upon her, Revelation 18:7.
(r) "erravit cor meum", Montanus; "errat animus meus", Junius & Tremellius; "errat cor meum", Piscator. (s) Vid. Herodot. l. 1. c. 191. Xenophon. l. 7. c. 23. (t) L. 1. c. 5. p. 24. Ed. Braithaupt.

panted--"is bewildered" [BARNES].
night of my pleasure--The prophet supposes himself one of the banqueters at Belshazzar's feast, on the night that Babylon was about to be taken by surprise; hence his expression, "my pleasure" (Isaiah 14:11; Jeremiah 51:39; Daniel. 5:1-31).

The night - In which I used to have sweet repose. He seems to have had this vision in a night. But withal this signified that horror and destruction, which should befal the Babylonians in a night of feasting and jollity. He - God, who shewed him that vision.