Research has revealed that many suspected Poltergeist agents are females under the age of 25, who are completely unaware that they are the causing this type of activity. Emotional problems associated with these individuals have been attributed to poltergeist activity, and include emotions such as anger, anxiety, paranoia, and schizophrenia. With psychological help the activities may diminish or even disappear completely with time.
Though the majority of Poltergeist cases are associated with unstable individuals, there are intermittent cases in which everybody involved is apparently stable from a psychiatric perspective. In these cases, the causes of Poltergeist activities remain unexplained
This site also has a great Glossary of Paranormal Terms where dozens of popular terms are explained in easy to understand short sentences.
The Paranormal Network:
The stress inherent in a poltergeist case, as well as the stress caused by one, does make counseling very important. Not only the agent, but all participants can benefit from individual or group counseling. Poltergeist activity tends to stop when the stress is identified, addressed or released, or when the stressful situation itself is identified, altered or ended. Poltergeist activity also tends to stop when the agent realizes he or she is responsible for the phenomena (and especially if the agent accepts responsibility for it).