Trance mediumship / communication occurs where the spiritual medium is able to withdraw within and disengage to a point from conscious control of their mind thus allowing it to function under the influence of a spirit communicator. You will find that some authors try to make distinctions between, overshadowing, light trance, or deep trance, or some such similar terms in an effort to distinguish between different levels of trance control. While the level of trance control does vary such terms and distinctions are only useful up to a point and can convey a mistaken impression that we can distinguish between these levels of trance in some definitive way and that there is an inherent difference in the quality of the communication.
However, it is generally accepted that when a spiritual medium is in deep trance they will not be consciously aware of the content of the communication while they have been in trance. The level of trance can however vary even for a deep trance medium during any one trance session. While it is to be hoped that there will be less interference from the medium's mind in deep trance there is also no reason to suppose that there is any more guarantee of the accuracy of the communication in the case of a deep trance medium. Whatever the level of trance the spirit communicators have to work through the medium's mental processes, conscious and unconscious.
The process involved in trance mediumship essentially involves a blending of energies; those of the medium with those of the spirit communicator. The blending may vary in degree and intensity. The spirit communicator does not necessarilly enter the physical space of the medium's body but can work through the medium's aura. However close the spirit approaches it is misleading to use such terms as "direct control". Whatever happens is with the permission of the medium and such terms can lead to a mistaken impression of the medium being "taken over" in some way. From the point of view of the audience it is easy to see how they may feel that the medium, in a medium to deep trance, has "gone" and they are talking directly to another person with different mannerisms, gestures, gender, age, tone of voice, accent, etc and to an extent this feel of the situation is correct.
A small minority of witnesses of trance mediumship are sometimes a little nervous at first. This is often due to the mistaken perception of the medium being fully "taken over" by a spirit and the associated feelings of uncertainty as to what to expect, especially if the person is sitting in the near vicinity of the medium. Horror movies indulging in flights of fantasy have further fuelled superstitious beliefs and fears. The reality is that the experience soon has a very natural and normal feel and becomes a friendly conversation amongst friends. The spirit communicators are good humoured, loving, and have a sense of fun. They enjoy interacting with people. It is just like having a conversation with anyone else, though they are generally more loving, patient and tolerant than the average person.