I tried to look this up on the Internet, and all the references I found are about so-called ‘demonic possession’. This may be a leftover from Christian and other religious prejudice which regard all such things as ‘demonic’ or of ‘the Devil’.
My own perception is that there are various kinds of possession or ‘walk-in’ phenomena.
The only kind which could be termed ‘demonic’, in my view, is when a lower spirit entity takes over a living human and encourages them to kill, sexually assault or injure other human beings. Even so these spirits are not ‘demons’ but simply those who have not evolved and whose spiritual realm should be the lower astral until they are able to regret their actions and evolve to higher spiritual dimensions.
The second category of this kind of phenomena is when an Earthbound spirit enters a living human to satisfy an addiction to alcohol, drugs, consensual sexual gratification with other adults, etc. I do not regard this as ‘demonic’ It is certainly an inability to move on, and if the host is unaware or unwilling to accommodate the spirit, it is unhealthy and an invasion of personal privacy.
The third category would be as Andrew Russell-Davis is experiencing with Diana, former Princess of Wales. An Earthbound spirit which feels it has a mission and also unfinished business on Earth. A mission to prove survival, for instance, and a desire to connect with loved ones on Earth and, in Diana’s case and possibly others, to add evidence to the circumstances of the death of their physical body. In this case the host may be willing to accommodate the spirit, sharing a sense of mission or of completing unfinished business.
All are examples of either possession or ‘walk-ins’ where a spirit, permanently or temporarily, enters a living human being or attaches itself to one.
Are all these forms of phenomena unhealthy? That is the real question. Should all spirits move on to the Spiritual dimensions and not remain Earthbound? Are some given permission to undertake a mission in this way? If so is this because the mission is planned by Higher Spirits or for educational/development purposes for the Earthbound spirit so they can learn to what extent remaining Earthbound and attached to a living human can achieve their stated purpose?
I try to keep an open mind, though tend toward the latter interpretation. There will come a time when all Earthbound spirits will decide it is time to move on, whether they are attached to a living human being or not. For the host of an attached spirit, whether willing or unwilling, I fear it may be unhealthy especially if it continues for a long period with little positive results. If very positive results are achieved, however, it could become very worthwhile for both the Earthbound spirit, the host and for other human beings on Earth.