The Early Sessions, Book 6

"Your waking consciousness only participates in projections as a rule when you are in a period of high vitality, and exceptional health. On occasion the waking consciousness does participate during other usually very depressed periods. But generally speaking high energy is needed in order to maintain overall stability, and in order that the ego is not overstrained ...It is the same with the conscious retention of dreams in general. You are indeed exercising what amounts to an added ability."

Session 277, Page 304