Mediumistic aspects in a dream can represent our wish to be in contact with the dead.
This does not necessarily have to be dead in literal terms, it can merely be what is ‘dead’ in our life, that which we may wish to resurrect. During spiritual development, our perceptions widen from the ordinary everyday to other aspects and dimensions of knowledge that have become available to us. Whether these are aspects of our own personality or of the spirit realm is immaterial, since ultimately their function is to help us progress.
The spiritual self has access to the collective unconscious in its entirety.