Lower spirits are those beings without physical forms whose sanskaras remain to be wiped out. They cannot progress after death until their unfinished sanskaras are worked out. As a consequence, they wander about on the lower Astral plane. For this reason, they are a source of harassment to living people.

Suppose a man is destined to have a life span of forty years, but he commits suicide when he is thirty. Consequently, for the remaining ten year period of unexpressed sanskaras, his spirit inhabits the lower planes, and at times is seen by some people as a spirit or ghost.

To hold seances or to talk with the dead is no great thing, because such spirits are always among us on this living plane. There are advanced yogis and munis who converse with these ghosts who have committed suicide, as well as with the spirits of the higher planes. These advanced souls communicate without using a medium. They live on both levels.
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Backbiters are your friends as they take over your bad sanskaras to themselves.