Paranoia is excessive concern about one's own well being, sometimes suggesting the person holds persecutory beliefs concerning a threat to themselves or their property.
In the original Greek παράνοια (paranoia) means self-referential, and it is this meaning which has been adopted in psychiatry, especially European psychiatry, in reference to a delusional belief (see delusions). Specifically, the term paranoia is used to denote a delusional belief that is self-referential (see also ideas of reference). The delusional belief may not necessarily be persecutory. For example, a person who has a delusional belief that they are an important figure (such as being Jesus, Napoleon, or the Dalai Lama) may be diagnosed as having a paranoid belief or, if they hold this belief in the context of schizophrenia, as having paranoid schizophrenia. Paranoia and delusions in general are considered an important (if not the most important) diagnostic feature of psychosis.
The term paranoia was previously used in psychiatry used to describe what is now called delusional disorder. That is, a mental illness that involves one or more non-bizarre delusions with the absence of any other psychopathology (signs or symptoms of mental illness).
Common paranoid delusions may include the belief that the person is being followed, poisoned or loved at a distance (often by a media figure or important person, a delusion known as erotomania or De Clerambault syndrome). Other common paranoid delusions include the belief that the person has an imaginary disease or parasitic infection (delusional parasitosis), that the person is on a special quest or has been chosen by God, that the person has had thoughts inserted or removed from conscious thought or that the person's actions are being controlled by an external force (see mind control).
Many despotic rulers (for example Stalin) allegedly suffered from paranoia. This presents an interesting question because in Stalin's case, it is quite likely that many people really were out to get him (some theories state he was finally poisoned). Might it be that with enough enemies, it is impossible to be clinically paranoid? This begs interesting philosophical questions about the criteria by which we can diagnose a belief as paranoid or delusional.
Clinically, paranoid beliefs can be categorised into a number of types, although these are now listed as sub-types of delusional disorder (see that article for more details).
In popular culture paranoia is often represented as including: