It is hardly surprising that at the end of this divine chastisement, all fall again to the earth. It was an overwhelming experience. Note that the idea of the voice of thunder and the shaking of the earth are repeated. Those were not incidental parts of the experience, but significant signs of the divine power that was present.
The result of the experience is that Alma becomes temporarily unable to speak. He is unable to walk or even move his hands. Therefore, he is taken to his father. Alma the elder recognizes the hand of God. Even facing a weakened son, he rejoiced because he understood that his son was in the throes of a spiritual transformation.