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Processwork is a post-Jungian approach to consciousness and dreaming which definitely straddles the line between mysticism and medicine. It's about taking Jung's idea of talking to one's dreams and applying it to waking experiences, group experiences and synchronicities. It happens to be good for exploring and working over both "the dark stuff" and "things we dissociate from, repress, oppress, or spend a lot of energy refusing to look at," for the same reason it works for looking at dreams.
If you want theory about it, the resource I recommend is "River's Way" by Arnold Mindell. He directly relates what he's working to alchemy, astrology and working with entities and mythic states of conciousness in that.
If you want application, I recommend "Your Unique Facilitator Style" by Amy Mindell. She has a bunch of exercises which guide the reader through some moderate shadow work without ever accusing the shadow bits of being bad, and a whole bunch of plant-art helpers scattered in the pages to help.
