A.T. Robertson Commentary John 18:6

"When therefore he said unto them, I am [he], they went backward, and fell to the ground." — John 18:6 (ASV)

Fell to the ground (επεσαν χαμα). Second aorist active indicative of πιπτω with first aorist ending (-αν). This recoil made them stumble. But why did they step back? Was it the former claim of Jesus (I am , εγω ειμ) to be on an equality with God (8:58; 13:19) or mere embarrassment and confusion or supernatural power exerted by Jesus? B adds Ιησους which must mean simply: "I am Jesus."