In popular culture, the term paranoia is usually used to describe excessive
concern about one's own well-being, sometimes suggesting a person holds
persecutory beliefs concerning a threat to themselves or their property and 
is
often linked to a belief in conspiracy theories.
The term is more typically used in a general sense to signify any delusion, 
or
more specifically, to signify a delusion involving the fear of persecution. 
The
exact use of the term has changed over time, and because of this, psychiatri
c
usage may vary.

Explanation

In psychiatry, the term paranoia was used by Emil Kraepelin to describe a me
ntal
illness in which a delusional belief is the sole, or most prominent feature.
 In
his original attempt at classifying different forms of mental illness, Emil
Kraepelin used the term pure paranoia to describe a condition where a delusi
on
was present, but without any apparent deterioration in intellectual abilitie
s
and without any of the other features of dementia praecox, the condition lat
er
renamed schizophrenia.
In the original Greek, paranoia means simply madness (para = outside;
nous = mind). Kraepelin developed a definition from this root involving
delusional beliefs. Notably, in his definition, the belief does not have to 
be
persecutory to be classified as paranoid, so any number of delusional belief
s
can be classified as paranoia. For example, a person who has the sole delusi
onal
belief that he is an important religious figure would be classified by Kraep
elin
as having 'pure paranoia'.
Although the diagnosis of pure paranoia is no longer used (having been
superseded by the diagnosis of delusional disorder) the use of the term to
signify the presence of delusions in general, rather than persecutory delusi
ons
specifically, lives on in the classification of paranoid schizophrenia, whic
h
denotes a form of schizophrenia where delusions are prominent.
More recently, the clinical use of the term has been used to describe delusi
ons
where the affected person believes they are being persecuted. Specifically, 
they
have been defined as containing two central elements:
The individual thinks that harm is occurring, or is going to occur, to him o
r
her.
The individual thinks that the persecutor has the intention to cause harm.
Paranoia is often associated with psychotic illnesses, particularly
schizophrenia, although attenuated features may be present in other primaril
y
non-psychotic diagnoses, such as paranoid personality disorder.

Examples of clinical paranoia

In the unrestricted use of the term, common paranoid delusions can include t
he
belief that the person is being followed, poisoned or loved at a distance (o
ften
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.
Many despotic rulers (for example Stalin) allegedly suffered from paranoia. 
This
presents an interesting question because in Stalin's case, it is quite likel
y
that many people really were out to get him (some theories concerning his de
ath
hypothesize that he was poisoned). The possibility exists that with enough
enemies, it is impossible to be clinically paranoid. It still might be possi
ble
to identify a paranoid in that situation via his unrealistic assessment of t
he
relative threat presented by various enemies, but it is not clear that
non-paranoid persons are all that good at this. This raises interesting
philosophical questions about the criteria by which we can diagnose a belief
 as
paranoid or delusional, as well as prompting the joke that "Just because you
're
paranoid doesn't mean they're not out to get you".

Paranoia depicted in popular culture

In popular culture paranoia is often represented as including:
Belief in having special powers or being on a special mission (a "delusion o
f
grandeur")
Conspiracy theories, such as seeing seemingly unrelated news events as parts
of a larger, typically conspiratorial plan
Black helicopters and other mass surveillance
Persecution from powerful adversaries such as UFOs, terrorists, the Men in
Black, secret societies or demons
Mind control through invisible rays, and tinfoil hats to combat them
Fear of poisoning, adulterated food (e.g., aspartame) or water (e.g.,
fluoridation) as part of a secret plot
Reading a story, watching a movie, or listening to a song and feeling that
one's life is exactly like that of the subject of said story, movie, or song
.
The movie The Truman Show, which depicted a man who discovers his entire lif
e
has been filmed as a TV show, is one of the more commonly referrenced films.
The maxim: Just because you're paranoid doesn't mean that they aren't really
out to get you.

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