In the story "To Build a Fire", why does the man decide to run?

The man ran out of fear, desperation, and an attempt to get warm. 

The fear made him lose control of himself and he turned and ran along the creek bed on the old trail. The dog joined him and followed closely behind. The man ran blindly in fear such as he had never known in his life. Slowly, as he struggled through the snow, he began to see things again—the banks of the creek, the bare trees, and the sky.

The running made him feel better. He did not shake any more. Maybe, if he continued to run, his feet would stop freezing. Maybe if he ran far enough, he would find the camp and the boys.