Some good explanations from http://www.texasghostandspirit.com. Just in time for Halloween.

To begin understanding the nature of parasite spirits, those that seem to attach themselves to and draw energy from individuals, consider the nature of spirits in general. First, spirits aren’t from around here: they are either tourists or invited guest that didn’t know when to go home. Either way, the material, physical universe is not their natural habitat.

Spirits, whether invited (summoned) or attracted to a place, a thing, or a living person, need energy to manifest in the physical world. Summoners, alone or in groups, raise the level of energy using it to attract and manifest a spirit. Those tied to a location are usually attracted by any event causing a sudden increase in emotions or a sharping of the focus of attention, either of which increases the energy level. The key element is the energy state of living things, it doesn’t have to be human, but must be alive.

With volumes of books on the subject, how spirits manifest is covered pretty extensively. Generally speaking, when summoned or attracted by events, spirits are bound or anchored by the conditions that bring them here. Our concern, are those spirits that have become unanchored. Summoned spirits can be unbound by accident or, in some cases, by design of the summoners. Location spirits can be unbound by the alteration or destruction of their domain.

Most will simply return home when the energy dissipates. Some will find other places with similar energies to move to. Of those that stay many will drift around collecting enough energy to sustain themselves, rarely interacting with the physical world around them to any noticeable degree. Usually there is no harmful intent and they pretty much leave us alone.

Parasites are like junkies; they’re hooked on the taste of energy. They are gluttons gorging themselves at our expense. The more they feed, the more they need.

Most siphon off your energy in a particular way. Whether by choice or by limitation, spirits tap specific energy centers (Chakra) or emotional centers. Over time, by manipulating the way energy flows through you, or by tapping strong emotional responses, a parasite can drain you dry. Given enough time a parasite’s drain can lead to physical illness or an emotional crisis just like physical parasites do.

Once they learn their way around spirits can manipulate your energy to reinforce the mode of energy they prefer. How you feel influences your decisions; the results of your choices influence how you feel. A well known pair, the Succubus and her brother the Incubus, live off sexual energy. To increase the harvest they try to keep lust high on the host’s priority list. It’s usually a lot more subtle than that, but you get the idea. You can become fixated on what the spirit needs your energy type and level to be and as soon as it gets its fill, suddenly you’re drained. It can look a lot like a manic/depressive cycle, but it isn’t and it happens over a relatively short space of time.

That influence is what makes a parasite spirit really dangerous. It is also what makes them vulnerable. Once the spirit and the influence are identified removing them entails working around the influence to change the energy flow. It gets more difficult the longer the spirit has been with the host. Essentially, however, the key to ridding yourself of one of these nasties is an awareness of the spirit’s interest, and a willingness to push it off, repeatedly in some cases.

Difference between attachment and possession

Attachment- A spirit or entity will watch and wait for a moment of weakness and literally attaches it’s self to a person, much like a leech. It then feeds of their energy over a period of time, slowly moving its way into the person until they become so weak that they are open for possession or become possessed.

Possession - is when a spirit or entity breeches your active free will in some way to get inside and take control of your body. Stronger entities don’t mess with the slow process of attachment they go straight for the prize.

Spirits and entities do not walk to up to a person and ask them if they want to be possessed. Instead, they find a weakness or a door through traditional family behavior or reckless behavior of the individual. The person’s active free will must be breached. They usually seduce a person with something simple and almost innocent unless they have done something that they have tremendous shame or guilt over.

They will solicit your active free-willing participation and this is how they gain control.

Just as a flower needs a particular environment to flourish and grow, so does the human soul and body, put it in a hostile and harsh environment, deprive it of what it needs, then you will watch it deteriorate slowly and eventual die. But unlike a flower, if a person survives the environment, they come out much stronger and wiser.

Note: Below symptoms can well be psychiatric or psychological changes; therefore, you must be wary when you look at these as signs of possession, also taking in count of possible drug use.

All of the symptoms can be a cry for help or signal the beginning of drug use or mental illness. When these are the only things present, seek  psychological counseling first, before even giving thought to the possibility of possession.

Many of these changes are normal, especially when dealing with teenagers. Do not automatically think of possession unless you have some reason to believe they are vulnerable to possession.

For example, if they have been performing rituals or dabbling in the occult and then you start noticing personality changes. However, the likelihood is that it is a natural problem, natural being psychiatric or psychological.

As you will see, there are many other indications of possession. Look for some of those before you give credence to the idea of possession.

In addition, never mention to someone undergoing personality changes that they might be possessed. You can plant a dangerous seed by doing that.

 Mental Changes Affecting Then Person:

1. Look for changes in personality. This is usually seen when the person is affable and suddenly becomes extremely quiet.

2. Someone who is normally very active suddenly becomes isolated.

3. Look for changes in sleep patterns.

4. Look for sudden weight loss or gain.

5. Look for changes in attitude and behavior, usually becoming hostile.

6. Someone who begins cursing a lot when that is out of character for them.

7. Notice if they suddenly have an aversion to religious objects. They may be a person who normally goes to Church but suddenly despises the thought.

8. Look for evidence of self-mutilation.

9. Look for changes in the way the person dresses.

10. Observe their personal hygiene and look for changes.

11. Look for evidence of occult materials in the room.

12. Look for destructiveness on the part of a person, especially if that destruction is of religious objects.

13. They may become abusive and threatening for no reason.

14. They may become violent. They often attempt to hurt animals.

15. The person may experience severe nightmares or night terrors.

16. They may perform acts of humiliation, such as urinating on themselves, etc.

17. They may be sexually pre-occupied. Exposing themselves to others.

18. Take note of what appears to be a different personality or multiple personalities.

19. Look for unusual changes in diet. Foods that were once favorites may now be repulsive to the person. They may eat foods that they once detested or may quit eating completely.

20. Take note if they seem to have blackouts in their memory.

Physical Changes Affecting The Person:

1. The person involved may go for long periods of time without blinking their eyes (can also indicate a neurological condition).

2. The person may appear catatonic (can also be a sign of mental illness).

3. The person speaks a language they could not possibly know (or speak with an unusual accent).

4. The person speaks in tongues.

5. The person will become completely rigid where they cannot be moved at all, even by multiple people.

6. Look for changes in the eyes. They may turn almost black like shark eyes.

7. Look for obvious changes in their features.

8. The person may possess inhuman strength.

9. The person may exhibit “precognition,” the ability to predict the future.

10. The person displays “retro cognition,” the ability to know about past events they should not know about.

11. The person may be able to know something about a person they have not met.

12. Their voice may change. It may go from high to low to guttural.

13. They may be able to tell what you are thinking.

14. They may move in some unusual way. For example, they may seem to glide instead of walk.

15. Writing or symbols may appear on the body in the form of welts and scratches. Look especially in areas they could not reach.

16. They may levitate.

17. Eye color may change.

18. There may be multiple voices coming from the person at the same time.

19. Take note if animals appear to be frightened of the person, especially if they begin acting fearful when there are personality changes in the person.

Note: Most of these symptoms can be related to medical or psychological conditions but some of them fall outside the realm of science. If you start to see a few items in this category, there maybe serious cause for concern.

At this point, you start to take items from the first and second category and see if they are consistent with items from the third category.

Obviously, some are more telling than others. You have to give weight to the values when you try to make a determination.

 Outward Manifestations:

1. Objects move around seemingly by themselves.

2. Objects may disappear and not be found again.

3. Objects may disappear and be found in another location.

4. Objects may disappear and later be found where they originally were.

5. Objects may appear from nowhere.

6. Knocking, banging or pounding may be heard throughout the house or in just one room.

7. Objects fly around as if they were thrown from unseen hands.

8. There may be knocks at the door but no one is ever there. These are often heard in threes, as this is a way of mocking the Holy Trinity. Ditto for doorbells.

9. Religious articles disappear or are destroyed. They may also be desecrated.

10. Growling may be heard but the source cannot be located.

11. There may be scratching sounds heard without an obvious source.

12. There may be foul odors that have no verifiable source. They may come and go.

13. Odd lights may be seen. They may shoot around a room.

14. Heavy furniture may move on its own.

15. There may be sightings of people or dark shadows that may or may not have form.

16. Odd-looking creatures may be seen.

17. Doors and drawers may open and close on their own.

18. Electrical appliances may turn on or off.

19. Spontaneous fires may start up.

20. Animals may become spooked and stay away from the targeted person altogether.

21. Animals may growl at something they see but you do not.

22. Any talk of God or religion may cause an outbreak of activity.

23. Glass may break for no reason.

24. Sounds of glass breaking may be heard but there is no evidence of it happening.

25. There may be sudden temperature changes, up and down although it is usually down. These can be recorded on a thermometer.

26. A person may suddenly become cold while the temperature remains constant. A thermometer may record a one to two degree drop in that person.

27. People may have a feeling of being watched or that they are not alone.

28. People may hear voices when no one is present.

29. People will often hear their name called only to find that no one is around. Sometimes, a couple will each think they heard the other call to them.

30. There may be a sensation of wind blowing even with the windows closed.

31. Lights will go off or not come on when turned on.

32. Apparent retaliation after some attempt to stop the activity.

33. Activity starts up when you attempt to say prayers.

34. Apparent retaliation if a clergyman has been to the home.

35. Physical attacks. It might be in the form of punching, scratching, biting, hair pulling, etc.

36. Psychological attacks. The entity knows your weaknesses and will try to exploit them. Someone who feels ashamed about something will have an increase in that emotion. The same is true for depression, anxiety and anything else you can think of.

37. Sexual assaults. This can run the gamut from fondling to actual penetration. This can occur in males as well as females.

38. Levitation of objects or people.

Note: Please don’t go thinking you’ve been possessed because you may have experienced some of the above in a haunted home. We are looking at this as a whole with symptoms from all 3 sections.

Before jumping to the conclusion of someone being possessed it is very important to take time to think rationally about the situation and eliminate any logical reasons for the experiences.

 Signs you may notice in yourself:

1. Feeling “beside yourself” or “above yourself”. Disconnected.

2. Feeling chronically ungrounded.

3. Out of character selfishness, hatefulness, greed, jealousy.

4. Feeling carried away by something avaricious during trance or dreaming.

5. Experiencing the feeling that something is just beside or behind you, you may feel a stabbing sensation or pressure.

6. Experiencing chronic distraction whenever you try to get centered or do something good for yourself. Also experiencing unusual and remarkable hurdles to this.

7. Compulsive behavior that is out of character.

8. Loss of good judgment.

9. Restlessness, forgetfulness, general lack of mental focus, chronic boredom, and depression.

10. Suicidal thoughts and behavior.

11. Obsessive thinking and behavior.

12. Self abusive behavior and/or body neglect.

13. Feeling lost or betrayed for no specific reason.

14. Feeling “driven” or “captive” emotionally or mentally by a cycle of anger, fear, resentment, or sadness. This also applies when it pertains to feeling held hostage by a person or idea.

15. Nightmares which recur; especially those which consume or color your thoughts most or all of the day following the dreaming.

16. Waking feeling suffocated or feeling that the darkness is smothering you.

17. Unreasoned fear.

18. Pain, pressure, paralysis or muscle spasms which have no medical explanation.

19. Cycles of events which amount to ongoing crisis, tragedy or stress.

20. Sleeping plenty, but awaking completely drained.

21. Cycles of interactions with others which recur and cause pain, i.e.: repeatedly choosing lovers who are abusive or abandoning. This can be more subtle too, such as choosing friends, who refuse, avoid or are unable to resolve conflicts and which always or nearly always result in eventual loss of or disconnection with the each friend made.

22. Recurring illness and/or chronic illness.

23. Impending sense of doom.

24. All or several signs combined which cycle over and over despite best efforts to resolve in usually effective ways. Each cycle ends in feeling drained and “mortally tired”, even feeling abused.

Note: Once again some of these symptoms can be related to medical or psychological conditions, a reaction to medication or illegal drug use or a reaction to a stressful or traumatic event that has happened to you.

Spirits can also project some of these experiences on to you without actually possessing you. It’s always important to think rationally about what you are experiencing; don’t be quick to jump to conclusions.