Any american/british/australian/te… can help me?!?

Hello, im brazilian and I wanna know why in the song Down (by Jay Sean) he says 'baby are you down down down.' ? Why don't he say 'baby you are down down down.' ? I learned that in affirmatives sentences we use Verb To Be after 'you' and in questions we use the verb before 'you'. But IT IS A AFFIRMATIVE sentence! Explain me please, im confused! :S