In order to journey to the other dimensions of existence a Shaman induces an altered state of consciousness in himself similar to a state of self-hypnosis called a state of flow. While in this state of flow, or Shamanic Trance, he is in complete control. He is able to take his consciousness and subtle bodies into nonphysical reality where he visits the heavens and hells of existence, communicates with and controls spirits, gains information, retrieves souls, and makes subtle changes in reality which may affect the physical world. Properties of the Shamanic altered state of consciousness are:
In a state of flow, you feel as if you have actually become one with the activity you are focused on. You may lose track of your body, emotions, sense of time and even of your physical location. When you are giving everything you can to a particular vision or challenge, you become free of fear and anxiety. You have no room in your consciousness for boredom. Many people who function in this way speak of it as a "drug free high" that comes from the rhythm that seems to be part and parcel of working at this l00% level. Many people relate to this to activities as simple as Zen and the Art of Tying Your Shoes, to something more complicated such as driving a car. There is an "automatic pilot" effect. When tying your shoe, you JUST tie your shoe. When driving you know where you are going and you are driving effectively and safely and yet your mind is not intensely focused on the road. This is still attention to detail and focus, but it is different than intense concentration. It is not the type of concentration that creates great mental strain. The easiest way to describe "state of flow" is that you function at a level of excellence with ease. (source)
The lighter trance states feel like those times when you are reading a book, or watching television or a movie, and are so engrossed that you are not aware of your surroundings. The deeper trances feel similar to how you feel when you are first waking up in the morning. You are aware that you are awake, your imagery is vivid and dreamlike, and you feel relaxed, calm, and good.
The ability to attain a and control a trance is the result of cumulative conditioning and mental training.
A weight lifter trains himself by practicing daily. He begins by lifting relatively light weights and progresses to heavier and heavier ones. Eventually he is able to lift a 200 pound weight above his head with relative ease. By working in this manner he has trained his muscles to respond according to his will. After he has reached his goal he can maintain the ability by practicing only two or three times per week. If he stops practicing entirely his muscles will gradually loose their conditioning and strength and, after a time, he will no longer be able to lift the weight. By reestablishing a routine of practice he will bring his ability back to where it was.
This same principle applies to the trance state. You train your mind to respond in accordance with your will in order to produce the ability to develop a deep trance. This is done by daily practice. It may take some time and effort to establish that ability, but once you have it you will be able to maintain it by practicing only once or twice per week. If you stop practicing entirely your ability will gradually lessen. Like the weight lifter you will need to begin a more regular practice in order to reestablish your abilities.
When you go into any trance you gradually progress from ordinary consciousness into deeper levels. It's convenient to have a means of measuring the depth of your trance, so the paragraphs that follow outline some of the symptoms found at various depths. For convenience sake I've divided the depths of trance into four major sections, and, using terms borrowed from the hypnotic sciences, called them the Hypnodial, Light, Medium, and Deep Trance states.
Each depth of trance has valuable uses. For example, in the Light and Medium Trances you can learn to begin practical Shamanic Journeying so that you can see, hear, touch and smell experiences in the worlds which border ours. In those trance states these journeys will feel similar to a fantasy or daydream and you may wonder if it is real, or just your imagination. As you train yourself to deepen the trance the journeys become more vivid, until, in the Deep Trance, they look and feel as though they are taking place in physical reality.
ADDENDUM:
The quote above by Bearwalker in the last sentence reads in part "...until, in the Deep Trance, they look and feel as though they are taking place in physical reality." If you follow the Shamanic Journey as outlined in the link below Zen, the Buddha, and Shamanism there is a relatively interesting tid-bit left unmentioned that is highly related. And that is when the Wanderling awakened the next morning in the trees there was actual in-reality beach sand gripped in the palm of his hand, yet the spot he was found was at least seven miles inland from any sandy beach and several thousand feet up the mountain. However, the night before sand was scooped on a pass over Lime Cay during the journey. For additional insight into a similar situation, except it is in the realm of things Zen, visit the Yasutani Hakuun Roshi webpage. Scroll down to the Addendum toward the bottom of the page. For more in a similar Zen vein see: Traveling to the Illusory Realm of the Great Void by Grand Master Shen-yen Lu. See also Do You Think Flying in the Sky Is Magical? by Venerable Master Hsing Yun.
Ellie Crystal in her Shamanism page listed below writes:
"Shamanic Flight, is in most instances NOT an experience of an inner imaginary landscape, but IS the shamans's flight beyond the limitations of the physical body."
That is to say, NOT "a look and feel," but actually taking place.
See Also: OBEAH Jamaica-based Afro-Caribbean Shamanism
Click here: SHAMANISM
As well as: ZEN, THE BUDDHA, AND SHAMANISM
And the more indepth: WHAT IS A SHAMAN?
The above edited extracts are from a paper wrtten by Joseph Bearwalker Wilson in 1978.It describes some theory of the trance state as it applies to shamanism. Copyright, 1978, 1995 by: