Daniel 10:9 (ESV)

9 Then I heard the sound of his words, and as I heard the sound of his words, I fell on my face in deep sleep with my face to the ground.

When this man begins to speak, it is too much for Daniel. He hears the mighty voice of this man. This sound and appearance overwhelm Daniel. It is so impressive that he falls down unconscious. He falls into a deep sleep. He lies on his stomach on the bank of the Tigris.