Excerpted from the book Tao and Longevity by Nan Huaijin
Does the spirit actually leave the body during the transformation of chi into shen?
…There are many [Taoist] descriptions of being pregnant for ten months, suckling the baby for three years, and facing the wall for nine years that have led some people to believe that successful meditation must involve astral projection. The supposition is that the spirit or divine self has a fetal body of its own which ultimately shoots out of the top of the head and ascends into heaven itself. To believe that this is the way of transforming chi into shen is a serious mistake.
According to the Tan Tao school, yang shen (or positive spirit) and yin shen (or negative spirit) may both account for the projection of the spirit from out of the body. Continue reading Astral Projection and Yin Shen: A Taoist Perspective