I imagine it's often a combination of both. Because when my mind is cranking upwards, I actually tend to become less productive, my head will be too far up in the clouds (stormy or sunny), and I will be obsessing over things that ultimately distract me form important work. I will also become far less patient and tolerant about annoyances involved in productive work and can easily develop a "whatever" attitude about it. So I don't think a high mood automatically equates to being more productive. I think that chances are, you are a naturally very productive person, but hypo/mania can allow one to push it too far, so when the hypo bottoms out, it's too much.