We do not know any more on the subject than is related in the Bible. The natural inference from the narrative is that the king was temporarily deprived of his reason, and insane people often do things as unnatural as eating grass. There is nothing improbable in the Biblical statement. On the other hand, some authorities suggest that the narrative means nothing more than that the king left his palace and the cares of state and lived the life of a peasant for seven years; or, as we might say, vegetated in rural seclusion; but the plain statement of the text is that generally accepted. Daniel 4:35-37 indicates that he became, at least outwardly, a believer in the true God.