Interesting Dream Structure

I had an interesting dream structure last night, dreaming inside a dream. At times I would be exclusively inside the inner dream, and at other times I would wake up from the inner dream and be in the outer dream. When I woke from the inner dream to the outer dream I had that feeling of "realizing that I had just been dreaming". In the outer dream, I found out that I talked and even sung in my sleep while I was in the inner dream. In reality I did not talk in my sleep at all.