Here’s a summary of what the Garuda Purana has to say about ghosts. It’s a really interesting book.

Ghosts

Garuda asked, But sometimes ghosts come and pester people. How do they manage to do that? How do they escape from hell?

In the same manner that prisoners escape from prison, answered Vishnu. They come and disturb their friends and relatives.

They return to their old houses and cause all sorts of illnesses, such as fever. They are positively delighted when people get headaches or cholera. The more they loved their dear ones when they were alive, the more harm they cause them as ghosts. It is in kaliyuga that one has all these ghosts. There were no such ghosts is satyayauga, dvaparayuga or tretayuga. These ghosts cause strife among friends and kill animals and children.

How does one know that ghosts are around? asked Garuda.

The signs are fairly obvious, repied Vishnu. Animals die and friends fight. There are sudden catastrophes. Children turn against their parents, brahmanas are criticised and there are bad harvests. Fire break out for no reason at all. Husband and wife fight all the time. These are all signs.

What does one do if one knows that there are ghosts around? asked Garuda.

I have already indirectly answered the questions, replied Vishnu. Perform a funeral ceremony for the ghost. But it is also good to consult someone who is learned in these matters, a diviner or astrologer (daivajna).

A ghost is a sinner. And a person who knows that there are ghosts around but does nothing about it, also becomes a sinner by contamination. In his next life such a person is born poor, diseased, without a living and does not have any sons. Or he may even be born as an animal. If nothing is done about the ghosts, the ghosts themselves realize after sometime that there is no hope for salvation in haunting people. Their only hope for salvation lies in returning to hell and serving out their terms of penance. So they return to hell and give up the haunting.

The worst form of ghost is a pishacha. They are very mischievous. They appear to their friends and relatives in all sorts of different forms, as bulls, horses and elephants. They make sleepers have nightmares. They frighten people . Sometimes pishachas appear and beg for food. At other times, they steal food and water. You will know a pishacha if you run into a cow or bull that talks in the human tongue. Friends and relatives discover that they are being carried (through the sky) to all sorts of different places by the pishacha.

If it is known that a pishacha is around , the first thing that is to be done is to bathe in a tirtha. A bliva tree is to be watered next. And finally a ceremony is to be performed, at which learned brahmanas are given grain.