The falling to the earth is indicative of being overcome by the spirit. In this occasion we have no description of appearing as dead, but the falling to the earth motion was apparently an understood action that showed the presence of the power of the spirit. Certainly if Alma the Younger fell to the earth when he was visited, all these people should also fall to the earth when the Messiah visited them. Nephi’s specific conclusion is to affirm that now the people remember that there were prophecies that the Messiah should come, and they realize that those prophecies have been fulfilled. The people had been conversing about the Messiah, but some thought it was an angel who had come to them. Now they all understand who it is, and they witness that understanding with the falling to the earth sign.