Albert Barnes Commentary Numbers 24:4

"He saith, who heareth the words of God, Who seeth the vision of the Almighty, Falling down, and having his eyes open:" — Numbers 24:4 (ASV)

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.