We grow up thinking that the only way a soul leaves a body is when it dies. That may not be entirely true. The term "Walk-in" was coined by American journalist and Christian psychic Ruth Montgomery. However, the walk-in experience has existed long before in ancient Hinduism.
During a walk-in experience, two individual souls agree to switch places. The first soul has gone as far as it can in its development and is ready to move on. The soul that has taken its place will serve in a different capacity than before. Normally, permission has been granted in order for this to take place. The other soul continues on its journey, either to be together with a loved one or be sent to another place to continue learning. They will at this point in time not be back here. Another way to call the experience is soul transference.
For a soul to come into these bodies, the soul which is already there has to want to leave. For many people, that is a wise decision. The body may be maimed in a horrible way through car accidents or other terrible events, or the person may be on the verge of suicide or actually try to kill themselves. These are the kinds of bodies the new 'soul' takes over to nourish and use to do their earthly work.
Walk-ins comes into an older body and takes over the memories of the body, bypassing all that school learning. Sometimes that's a good thing, but its hard at the same time, because the body usually hasn't had the type of learning that the new 'soul' needs and relationships the body has had may not be of the type that the new 'soul' needs either and many walk-ins, if they are married, end up in divorce. Sometimes they don't even know the people in the family they come into and that's even more devastating on the walk-in.
Many walk-ins claim heightened psychic sensitivity and may take up work as New Age healers or ministers. Others claim inability to accomplish basic tasks of daily living. Clearly, at least for some, claiming a walk-in experience may have a number of secondary gains. In Ruth Montgomery's book Strangers Among Us noted her own walk-in experiences as well as some renowned figures such as Thomas Jefferson as having hosted walk-in spirits who actually wrote the Declaration of Independence.
Checklists to determine walk-in status include name changes, career changes, new interest in the study of psychic phenomena, a feeling that one is an alien, or a sudden desire to move to a new environment. Reported physical changes include memory loss and the sudden onset of allergic reactions. Since all of these factors could possibly be attributed to simple life changes such as adolescence or middle age, it's difficult to determine solely from such a checklist if a "true" walk-in has occurred. The most logical method might be to determine if any specific event historically connected with walk-ins (anaesthesia for surgery is one of the most common) occurred around the time one first started feeling differently. There is, however, no known scientific method to prove whether or not the walk-in experience has any objective reality, let alone how to determine if one has occurred.
Walk-in experiences are not regarded favorably by some religious groups and mental health professionals. Fundamentalist Christians denounce the walk-in idea as being connected with the occult. George Ganaway and other psychiatrists have written papers and given presentations reflecting their belief that all of these experiences, from traditional walk-ins to the New Age variety up to and including cooperative healthy multiples are mere attention-seeking and/or play-acting, or at best a "metaphor of distress" to express something the client feels is wrong, or somehow different from usual, but is having trouble describing.
Do you believe the walk-in experience is real or just a way to describe unexplainable behavior?
Source: Wikipedia and Dreams of the Great Earth Changes