I'm sorry I haven't replied in a long time, cause I was kinda busy these days with my finals... But anyway, I think that each variation has their own unique characteristic... it really reflects what Bach percieves about sleep, or the way to cure insomnia. I think individually, the variations won't stand a chance as anything difficult in the piano world, but together, they really mean alot, almost like what achievements and dilemmas a nobleman would experience in a lifetime.