I have this when I've been awake too long and am very tired, or, when I've just woken up and my mind is still dreaming. I can play entire songs in my head duri

I have this when I've been awake too long and am very tired, or, when I've just woken up and my mind is still dreaming. I can play entire songs in my head during those drowsy moments, but once fully awake/alert, I lose the ability.