Excellent question and I hope you get lots of well experienced replies.
The question strikes me as important because we spend, ideally, 8 hours sleeping in which, according to Tibetan Buddhism, we are essentially going through practice runs of the Bardo after life. Physically, the restorative processes for the muscular, neurologic, skeletal and all other systems are also vital. So I have to assume that the role of Chi here is huge and that there is a potential to prepare sleep, through some kind if Qigong, to get Chi flow more productive.
Right now, the only thing I found is essentially longevity breathing plus awareness of body tension (is this outer dissolution?). This is essentially the meditation taught by Eckhart Tolle or what new-agers call “body of light”.
Others please share your thoughts?