Master Lü-tsu said, Your work will gradually become concentrated and mature, but before you reach the condition in which you sit like a withered tree before a cliff, there are still many possibilities of error which I would like to bring to your special attention. These conditions are recognized only when they have been personally experienced […] In meditating, a man must have a sort of conscious intuition, so that he feels energy and breathing unite in the field of the Elixir; he must feel that a warm release belonging to the true light is beginning to stir dimly. Then he has found the right space. When this right space has been found, one is freed from the danger of getting into the world of illusory desire or dark demons.

Meditation, Stage 3: Separation of the spirit-body for independent existence.

Master Lü-tsu said, There are many kinds of confirmatory experiences. One must not content oneself with small demands but must rise to the thought that all living creatures have to be redeemed. One must not be trivial and irresponsible in heart, but must strive to make deeds prove one’s words.
 If, when there is quiet, the spirit has continuously and uninterruptedly a sense of great joy as if intoxicated or freshly bathed, it is a sign that the hght-principle is harmonious in the whole body; then the Golden Flower begins to bud. When, furthermore, all openings are quiet, and the silver moon stands in the middle of heaven, and one has the feeling that this great earth is a world of light and brightness, that is a sign that the body of the heart opens itself to clarity. It is a sign that the Golden Flower is opening.
 The Secret of the Golden Flower