The visions that develop in the bardo state, and the brilliant colours and sounds that come along with the visions, are not made out of any kind of substance which needs maintenance from the point of view of the perceiver, but they just happen, as expression of silence and expression of emptiness. In order to perceive them properly, the perceiver of these visions cannot have fundamental, centralised ego. Fundamentally ego in this case is that which causes one to meditate or perceive something.
If there were a definite perceiver, one could have a revelation of a god or external entity, and that perception could extend almost as far as a non-dualistic level. Such perception becomes very blissful and pleasant, because there is not only the watcher but also something more subtle, a basic spiritual entity, a subtle concept or impulse, which looks outwards. It begins to perceive a beautiful idea of wideness and openness and blissfulness, which invites the notion of oneness with the universe. This feeling of the openness and wideness of the cosmos would become very easy and comfortable to get into. It is like returning to the womb, a kind of security. Because of the inspiration of such a union, the person becomes loving and kind naturally, and speaks in a beautiful language. Quite possibly some form of divine vision could be perceived in such a state, or flashes of light or music playing, or some presence approaching.
In the case of such a person who relates to himself and his projections in that way, it is possible that in the after death period of the bardo state he might be extremely irritated to see the visions of the tathagatas, which are not dependent upon his perception. The vision of the tathagatas do not ask for union at all, they are terribly hostile; they are just there, irritatingly because they will not react to any attempts to communicate.
The first vision that appears as the vision of the peaceful divinities; not peacefulness in the sense of the love and light experience we have just been talking about, but of completely encompassing peace, immovable, invincible peace, the peaceful state that cannot be challenged, that has no age, no end, no beginning. This symbol of peace is represented in the shape of a circle; it has no entrance, it is eternal.
Not only in the bardo experience after death alone, but also during our lifetime, similar experiences occur constantly. When a person is dwelling on that kind of union with the cosmos – everything is beautiful and peaceful and loving – there is a possibility of some other element coming in, exactly the same as the vision of the peaceful divinities. You discover that there is a possibility of losing your ground, losing the whole union completely, losing your identity as yourself, and dissolving into an utterly and completely harmonious situation, which is, of course, the experience of the luminosity. This state of absolute peacefulness seems to be extremely frightening, and there is often the possibility that one’s faith might be shaken by such a sudden glimpse of another dimension, where even the concept of union is not applicable any more.
– Chogyam Trungpa, Commentary on The Tibetan Book Of The Dead
Cosmic Flotsam 