Dream on a loop

My friend told me about the worst nightmare he had ever had.

In the dream he was walking alone in a desert. Somehow he was carrying a spear in his hand…After some time he saw someone crouching on the sand in the distance. As he had been feeling quite lonely he quickly ran up to the man. But when he bent over to help him up he saw that the man was no other than himself. In an instant he was overcome with fear and without further thought hacked the man to death with the spear. He then started running, trying to get away as far from the place as possible. However he soon stumbled and sprained his ankle. There was nothing he could do except crouch down and stay still -. And while he was at it he casually looked up and spotted, in the distance, his double walking towards him with a spear in his hand… then he woke up.