Some commentators worry themselves about the fact that Daniel 4 is a mixture of first person account (Nebuchadnezzar speaking) and third person account (another narrator, writing about Nebuchadnezzar). They think this indicates that Daniel 4 was originally two different accounts, clumsily edited into what we now have.
Whether or not there were multiple original accounts we’ll never know: We have no documentary evidence for it at all.
However, Ernest Lucas, in his fine commentary on Daniel, shows how the writing or editing is far from clumsy for using different narrators. In fact, the reverse is the case: The switch between first and third person is actually a brilliant literary device to guide the reader to the intended message of the chapter.
Here are a couple of extracts:
“The use of the third person in vv. 28-33 is to be understood as a literary device to show that the king himself was unable to give an account of what happened to him while he was out of his mind.” (104)
“To this, one can add that the switch from first to third person occurs at what, in structural terms, is the mid-point and turning-point of the narrative. Up to this point, Nebuchadnezzar appears as the one who is in control, seemingly of the world as well as of his own fate. The beginning of the interpretation, signalled by Daniel’s appalled reaction to the dream, is the beginning of the demonstration that in reality, someone else, the Most High God, is in control both of the world and of Nebuchadnezzar’s fate. So, at this point, Nebuchadnezzar loses ‘control’ of the narrative to an anonymous narrator.” (104)