The subconscient during sleep remains in the body. The being really goes out into different planes of consciousness but its experiences are not kept in the memory, because the recording consciousness is too submerged to carry the record to the waking mind.
There is a change or reversal of the consciousness that takes place and the dream consciousness in disappearing takes away its scenes and experiences with it. This can sometimes be avoided by not coming out abruptly into the waking state or getting up quickly, but remaining quiet for a time to see if the memory remains or comes back. Otherwise the physical memory has to be taught to remember.
Dream experiences can have a great value in them and convey truths that are not so easy to get in the waking state.
Everything should be for the sake of the Divine. As for leaving the result to the Divine, it depends on what you mean by the phrase. If it implies dependence on the Divine Grace and equanimity and patience in the persistent aspiration, then it is all right. But it must not be extended to cover slackness and indifference in the aspiration and endeavour.