The "falling" of which Balaam speaks was the condition under which the inward opening of his eyes took place. It indicates the force of the divine inspiration overpowering the seer. The faithful prophets of the Lord do not appear to have been subject to these violent illapses Daniel 8:17; Revelation 1:17.
In Balaam and in Saul 1-Samuel 19:24 the word of God could only prevail by first subduing the alien will, and overpowering the bodily energies which the will ordinarily directs.

Falling into a trance - There is no indication in the Hebrew that he fell into a trance; these words are added by our translators, but they are not in the original. נפל nophel is the only word used, and simply signifies falling, or falling down, perhaps in this instance by way of religious prostration.

He hath said, which heard the words of God, which saw the vision of the Almighty, (c) falling [into a trance], but having his eyes open:
(c) Though he lay as in a sleep, yet the eyes of his mind were open.

He hath said, which heard the words of God,.... God speaking to him, which he did several times, and with which he was greatly elated, see Numbers 22:9,
which saw the vision of the Almighty; not that he had a sight of any similitude of God, though the angel that appeared to him, which was Christ the uncreated angel, might appear in an human form, for some visible form was seen both by the ass and him; but rather this respects the visions of God to him in the night; it may be in a dream, as has been already observed, and which the following words seem to confirm:
falling into a trance, but having his eyes open: or falling into a deep sleep, and yet the eyes of his body open, which sometimes is the case with persons asleep; or the eyes of his mind open, to receive the instructions given him in a dream or vision of the night; unless this is to be understood of his falling on his face, when he had his vision, as sometimes the prophets did, see Ezekiel 1:28, so the Targums of Jonathan and Jerusalem paraphrase it; and the latter says, he prophesied of himself, that he should fall by the sword; which is better than to interpret it of his falling when his ass lay down with him, as some do: so men may have a great deal of light and knowledge in their heads, and yet not have true grace in their hearts; great gifts, which puff up with pride and vanity, but not sanctifying grace, which is of an humbling nature, 1-Corinthians 8:1, what he said under a spirit of prophecy follows.

The vision - So called properly, because he was awake when this was revealed to him: A trance - Or, extasy, fainting and falling upon the ground, as the prophets used to do.