What Happened in the Dream?

Shankara Chariya says, not one drop of sand in the desert can be made wet by the water of the mirage. An unreal oasis can exist with a real desert. An unreal snake can coexist with a real rope. Unreality and reality have no clash. But does the real level of,. the higher level of existence, does it affect the lower level of experience? Yet it does. How it forms the basis of that? Unless you are a waker, you cannot go to sleep and dream.Unless there is a real desert, the false oasis cannot, mirage cannot appear. Unless there is areal rope, the false snake cannot appear there.