There's an old cliche that states that just before you die, your whole life "flashes before your eyes." As no one who has died has come back to tell what he or she saw in those last seconds or minutes of life, the veracity of the cliche is yet to be categorized as fact.
In the case of Peyton Farquhar, we are given a glimpse of the condemed man's last moments of life. We see the soldiers with their guns and the early morning mist, and the bridge, and Farquhar, and the river below. All this is real and present. The noose is put around his neck and then his body drops. This, too, is real and present.
But from the time the noose breaks and Farquhar falls into the river up to the time he runs to the waiting arms of his wife, all we see is in Farquhar's mind. We were watching the dying man's last dream, what he wishes would happen flashes before his eyes.
Then we see the tight rope and noose and Farquhar dangling from it, swaying over the river. We are shocked back to the present... back to what is actual and real.