Good idea.
I'm not sure many people would use it to actually help them fall asleep but it's a funny concept.
As many others have said, more than two backrounds would be nice.
Some people find certain sounds more soothing than music, such sounds of the jungle, the ocean, a creek, birds, ect... So in addition to music you could put some of those in there.
Also as far as music goes, some of your choices weren't what I would call relaxing, I find Motzart relaxing personally, perhaps some music more like that?
Better animation, just watching sheep and stars rotate isn't enough. You need to give the eyes a whole lot more to do. Instead of the stars rotating you could have them flicker in seemingly random intervols. Also the occational shooting star would be nice.
As far as the sheep go, their running should be a little more realistic, and a tiny bit faster wouldn't hurt either. Their jumping also could be more realistic.
Perhaps you could put some trees in and have the wind blowing them back and forth ever so slightly?
Some additional landscapes could be different times of the year, for fall you could have leaves falling from trees, for whinter you could have snow falling. And for any season the occational cloud floating by wouldn't hurt. Maybe more for different seasons?
Mix up the sheep a little, don't make them all the same.
As I said this is a good idea, it just needs some refinement. Hope I helped and good luck on your next one :)