Sometimes I'm dreaming... (grammar)
You know, there is this awesome British rock band The Cure. And there is this awesome song they sang in the early 80-s called "Sharlotte Sometimes". In that song there is this strange line "Sometimes I'm dreaming".
So, why present continuous? What's the meaning of the tense in this case? Is it used to make the narration more vivid? The description more emotional? ...Or anything?

Question

Sometimes I'm dreaming... (grammar)
You know, there is this awesome British rock band The Cure. And there is this awesome song they sang in the early 80-s called "Sharlotte Sometimes". In that song there is this strange line "Sometimes I'm dreaming". 
So, why present continuous? What's the meaning of the tense in this case? Is it used to make the narration more vivid? The description more emotional? ...Or anything?

Answer

Well, Robert Smith wrote it based on the book Charlotte Sometimes, so it's highly plausible that those exact words are lifted straight from the book.

You're right insofar that "sometimes I dream" is grammatically proper, but Smith's line still works on a grammatical level, that is to say, the action is prolonged or repeated.

Now I'm singing it in my head.

Answer

This is called " poetic licence." Writers often use incorrect grammar to fit into a certain rhyme scheme.