I think I know exactly what you are talking about. This letting go feeling is different for everyone, some people feel like they are falling through their beds, others feel various other things. Personally I feel a change in my body shape and position, as if my body has almost disintigrated and then reformed anew but different from the old, and at times I also feel like I am floating above my bed freely. I never open my eyes during these phases so I don't know exactly what is going on but if I remain calm and aware throughout the SP, I end up transitioning into a dream inside my own room without having to visualize anything or try hard at all. I think you should read a thread I posted a while ago titled "Shapeshifting into WILD (help for those misunderstanding transition)" In that thread I talk about exactly what I feel when I transition and "let go" into a WILD. If you have any further questions after reading that, feel free to PM me.