I am studying the practice of trancing in the religious ceremonies of certain cultures, and I became curious about some of the perceptual and physical experiences that occur during the trance state. The first stage features entoptic phenomena - the shaman experiences brightly lit patterns during the first phase of altered consciousness. My teacher said this is not unlike what you might see when pressing on the corner of your eye. All I really know is that the effects are produced by the central nervous system, but I wonder what triggers this. I have also read that nosebleeds are a very common occurrence during the trance state. I was very curious about that. I have seen people undergo the trance state and films and they sometimes shake violently. Do you think the nosebleed is related to that?