A fixed fantasy — also known as a "dysfunctional schema" — is a belief or system of beliefs held by a single individual to be genuine, but that cannot be verified in reality. The term is typically applied to individuals suffering from some type of psychiatric dysregulation, most often a personality disorder.

The term is also used in the different context of psychoanalysis to distinguish between 'a normal transitory one and a fixed fantasy' with respect to the phantasised 'fulfilment in conscious or unconscious thought of the sexualised wish'.

Diagnostic criteria have been proposed for ORS:

- Persistent (> six months), false belief that one emits an offensive odor, which is not perceived by others. There may be degrees of insight (i.e. the belief may or may not be of delusional intensity).

- This pre-occupation causes clinically significant distress (depression, anxiety, shame), social and occupational disability, or may be time-consuming (i.e. preoccupies the individual at least one hour per day).

- The belief is not a symptom of schizophrenia or other psychotic disorder, and not due to the effects of medication or recreational drug abuse, or any other general medical condition.

The Truman Show delusion, informally known as Truman syndrome, is a type of delusion in which the person believes that their lives are staged reality shows, or that they are being watched on cameras. The term was coined in 2008 by brothers Joel Gold and Ian Gold, a psychiatrist and a neurophilosopher, respectively, after the film "The Truman Show".

The Truman Show delusion is not officially recognized nor listed in the "Diagnostic and Statistical Manual of the American Psychiatric Association".

Folie à deux (; ; French for "madness of two"), or shared psychosis, is a psychiatric syndrome in which symptoms of a delusional belief and sometimes hallucinations are transmitted from one individual to another. The same syndrome shared by more than two people may be called "folie à trois", "folie à quatre", "folie en famille" ("family madness"), or even "folie à plusieurs" ("madness of many").

Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-IV – 297.3) and induced delusional disorder (F24) in the ICD-10, although the research literature largely uses the original name. This disorder is not in the current DSM (DSM-5). The disorder was first conceptualized in 19th-century French psychiatry by Charles Lasègue and Jean-Pierre Falret and is also known as Lasègue-Falret syndrome.

Erotomania is a type of delusional disorder where the affected person believes that another person is in love with him or her. This belief is usually applied to someone with higher status or a famous person, but can also be applied to a complete stranger. Erotomanic delusions often occur in patients with schizophrenia and other psychotic disorders, but can also occur during a manic episode in the context of bipolar I disorder. During an erotomanic delusion, the patient believes that a secret admirer is declaring his or her affection for the patient, often by special glances, signals, telepathy, or messages through the media. Usually the patient then returns the perceived affection by means of letters, phone calls, gifts, and visits to the unwitting recipient. Even though these advances are unexpected and often unwanted, any denial of affection by the object of this delusional love is dismissed by the patient as a ploy to conceal the forbidden love from the rest of the world.

Erotomania is also called de Clérambault's syndrome, after French psychiatrist Gaëtan Gatian de Clérambault (1872–1934), who published a comprehensive review paper on the subject ("Les Psychoses Passionnelles") in 1921. Erotomania should not be confused with obsessive love or obsession with unrequited love, neither of which involves delusion.

This syndrome is most commonly diagnosed when the two or more individuals concerned live in proximity and may be socially or physically isolated and have little interaction with other people. Various sub-classifications of "folie à deux" have been proposed to describe how the delusional belief comes to be held by more than one person :

- Folie imposée is where a dominant person (known as the 'primary', 'inducer' or 'principal') initially forms a delusional belief during a psychotic episode and imposes it on another person or persons (known as the 'secondary', 'acceptor' or 'associate') with the assumption that the secondary person might not have become deluded if left to his or her own devices. If the parties are admitted to hospital separately, then the delusions in the person with the induced beliefs usually resolve without the need of medication.

- Folie simultanée describes either the situation where two people considered to suffer independently from psychosis influence the content of each other's delusions so they become identical or strikingly similar, or one in which two people "morbidly predisposed" to delusional psychosis mutually trigger symptoms in each other.

Folie à deux and its more populous cousins are in many ways a psychiatric curiosity. The current Diagnostic and Statistical Manual of Mental Disorders states that a person cannot be diagnosed as being delusional if the belief in question is one "ordinarily accepted by other members of the person's culture or subculture" (see entry for delusion). It is not clear at what point a belief considered to be delusional escapes from the "folie à..." diagnostic category and becomes legitimate because of the number of people holding it. When a large number of people may come to believe obviously false and potentially distressing things based purely on hearsay, these beliefs are not considered to be clinical delusions by the psychiatric profession and are labelled instead as mass hysteria.

Differential diagnosis includes ruling out other causes such as drug-induced conditions, dementia, infections, metabolic disorders, and endocrine disorders. Other psychiatric disorders must then be ruled out. In delusional disorder, mood symptoms tend to be brief or absent, and unlike schizophrenia, delusions are non-bizarre and hallucinations are minimal or absent.

Interviews are important tools to obtain information about the patient's life situation and past history to help make a diagnosis. Clinicians generally review earlier medical records to gather a full history. Clinicians also try to interview the patient's immediate family, as this can be helpful in determining the presence of delusions. The mental status examination is used to assess the patient's current mental condition.

A psychological questionnaire used in the diagnosis of the delusional disorder is the Peters Delusion Inventory (PDI) which focuses on identifying and understanding delusional thinking. However, this questionnaire is more likely used in research than in clinical practice.

In terms of diagnosing a non-bizarre delusion as a delusion, ample support should be provided through fact checking. In case of non-bizarre delusions, Psych Central notes, "All of these situations could be true or possible, but the person suffering from this disorder knows them not to be (e.g., through fact-checking, third-person confirmation, etc.)."

Because it is a rare and poorly understood condition, there is no definitive way to diagnose the Capgras delusion. Diagnosis is primarily made on psychological evaluation of the patient, who is most likely brought to a psychologist's attention by a family member or friend believed to be an imposter by the person under the delusion.

The core symptom of the disorder is that the sufferer holds an unshakable belief that another person is secretly in love with them. In some cases, the sufferer may believe several people at once are "secret admirers". The sufferer may also experience other types of delusions concurrently with erotomania, such as delusions of reference, wherein the perceived admirer secretly communicates his or her love by subtle methods such as body posture, arrangement of household objects, and other seemingly innocuous acts (or, if the person is a public figure, through clues in the media). Erotomanic delusions are typically found as the primary symptom of a delusional disorder or in the context of schizophrenia and may be treated with atypical antipsychotics.

The differential diagnosis for ORS may be complicated as the disorder shares features with other conditions. Consequently, ORS may be misdiagnosed as another medical or psychiatric condition and "vice versa".

The typical history of ORS involves a long delay while the person continues to believe there is a genuine odor. On average, a patient with ORS goes undiagnosed for about 8 years. Repeated consultation with multiple different non-psychiatric medical specialists ("doctor shopping") in an attempt to have their non-existent body odor treated is frequently reported. Individuals with ORS may present to dermatologists, gastroentrologists, otolaryngologists, dentists, proctologists, and gynecologists. Despite the absence of any clinically detectable odor, physicians and surgeons may embark on unnecessary investigations (e.g. gastroscopy), and treatments, including surgery such as thoracic sympathectomy, tonsillectomy, etc. Such treatments generally have no long-term effect on the individual's belief in an odor symptom. If non-psychiatric clinicians refuse to carry out treatment on the basis that there is no real odor and offer to refer them to a psychologist or psychiatrist, persons with ORS typically refuse and instead seek "a better" doctor/dentist.

Conversely, some have suggested that medical conditions which cause genuine odor may sometimes be misdiagnosed as ORS. There are a great many different medical conditions which are reported to potentially cause a genuine odor, and these are usually considered according to the origin of the odor, e.g. halitosis (bad breath), bromhidrosis (body odor), etc. These conditions are excluded before a diagnosis of ORS is made. Although there are a multitude of different publications on topics like halitosis, the symptom is still poorly understood and managed in practice. It is recognized that symptoms such as halitosis can be intermittent, and therefore may not be present at the time of the consultation, leading to misdiagnosis. Individuals with genuine odor symptoms may present with similar mindset and behavior to persons with ORS. For example, one otolaryngologist researcher noted "behavioral problems such as continuous occupation with oral hygiene issues, obsessive use of cosmetic breath freshening products such as mouthwashes, candies, chewing gums, and sprays, avoiding close contact with other people, and turning the head away during conversation" as part of what was termed ""skunk syndrome"" in patients with genuine halitosis secondary to chronic tonsillitis. Another author, writing about halitosis, noted that there are generally 3 types of person that complain of halitosis: those with above average odor, those with average or near-average odor who are oversensitive, and those with below average or no odor who believe they have offensive breath. Therefore, in persons with genuine odor complaints, the distress and concern may typically be out of proportion to the reality of the problem. Genuine halitosis has been described as a social barrier between the individual and friends, relatives, partners and colleagues, and may negatively alter self-esteem and quality of life. Similar psychosocial problems are reported in other conditions which cause genuine odor symptoms. In the literature on halitosis, emphasis is frequently placed on multiple consultations to reduce the risk of misdiagnosis, and also asking the individual to have a reliable confidant accompany them to the consultation who can confirm the reality of the reported symptom. ORS patients are unable to provide such confidants as they have no objective odor.

Various organic diseases may cause parosmias (distortion of the sense of smell). Also, since smell and taste are intimately linked senses, disorders of gustation (e.g. dysgeusia- taste dysfunction) can present as a complaint related to smell, and "vice versa". These conditions, collectively termed chemosensory dysfunctions, are many and varied, and they may trigger a person to complain of an odor than is not present, however the diagnostic criteria for ORS require the exclusion of any such causes. They include pathology of the right hemisphere of the brain, substance abuse, arteriovenous malformations in the brain, and temporal lobe epilepsy.

Social anxiety disorder (SAD) and ORS have some demographic and clinical similarities. Where the social anxiety and avoidance behavior is primarily focussed on concern about body odors, ORS is a more appropriate diagnosis than avoidant personality disorder or SAD. Body dismorphic disorder (BDD) has been described as the closest diagnosis in DSM-IV to ORS as both primarily focus on bodily symptoms. The defining difference between the two is that in BDD the preoccupation is with physical appearance not body odors. Similarly, where obsessive behaviors are directly and consistently related to body odors rather than anything else, ORS is a more appropriate diagnosis than obsessive compulsive disorder, in which obsessions are different and multiple over time.

ORS may be misdiagnosed as schizophrenia. About 13% of schizophrenics have olfactory hallucinations. Generally, schizophrenic hallucinations are perceived as having an imposed, external origin, while in ORS they are recognized as originating from the individual. The suggested diagnostic criteria mean that the possibility of ORS is negated by a diagnosis of schizophrenia in which persistent delusions of an offensive body odor and olfactory hallucinations are contributing features for criterion A. However, some reported ORS cases were presented as co-morbid. Indeed, some have suggested that ORS may in time transform into schizophrenia, but others state there is little evidence for this. Persons with ORS have none of the other criteria to qualify for a diagnosis of schizophrenia.

It has been suggested that various special investigations may be indicated to help rule out some of the above conditions. Depending upon the case, this might include neuroimaging, thyroid and adrenal hormone tests, and analysis of body fluids (e.g. blood) with gas chromatography.

The modern definition and Jaspers' original criteria have been criticised, as counter-examples can be shown for every defining feature.

Studies on psychiatric patients show that delusions vary in intensity and conviction over time, which suggests that certainty and incorrigibility are not necessary components of a delusional belief.

Delusions do not necessarily have to be false or 'incorrect inferences about external reality'. Some religious or spiritual beliefs by their nature may not be falsifiable, and hence cannot be described as false or incorrect, no matter whether the person holding these beliefs was diagnosed as delusional or not.

In other situations the delusion may turn out to be true belief. For example, in delusional jealousy, where a person believes that their partner is being unfaithful (and may even follow them into the bathroom believing them to be seeing their lover even during the briefest of partings), it may actually be true that the partner is having sexual relations with another person. In this case, the delusion does not cease to be a delusion because the content later turns out to be verified as true or the partner actually chose to engage in the behavior of which they were being accused.

In other cases, the delusion may be assumed to be false by a doctor or psychiatrist assessing the belief, because it "seems" to be unlikely, bizarre or held with excessive conviction. Psychiatrists rarely have the time or resources to check the validity of a person’s claims leading to some true beliefs to be erroneously classified as delusional. This is known as the Martha Mitchell effect, after the wife of the attorney general who alleged that illegal activity was taking place in the White House. At the time, her claims were thought to be signs of mental illness, and only after the Watergate scandal broke was she proved right (and hence sane).

Similar factors have led to criticisms of Jaspers' definition of true delusions as being ultimately 'un-understandable'. Critics (such as R. D. Laing) have argued that this leads to the diagnosis of delusions being based on the subjective understanding of a particular psychiatrist, who may not have access to all the information that might make a belief otherwise interpretable. R. D. Laing's hypothesis has been applied to some forms of projective therapy to "fix" a delusional system so that it cannot be altered by the patient. Psychiatric researchers at Yale University, Ohio State University and the Community Mental Health Center of Middle Georgia have used novels and motion picture films as the focus. Texts, plots and cinematography are discussed and the delusions approached tangentially. This use of fiction to decrease the malleability of a delusion was employed in a joint project by science-fiction author Philip Jose Farmer and Yale psychiatrist A. James Giannini. They wrote the novel "Red Orc's Rage", which, recursively, deals with delusional adolescents who are treated with a form of projective therapy. In this novel's fictional setting other novels written by Farmer are discussed and the characters are symbolically integrated into the delusions of fictional patients. This particular novel was then applied to real-life clinical settings.

Another difficulty with the diagnosis of delusions is that almost all of these features can be found in "normal" beliefs. Many religious beliefs hold exactly the same features, yet are not universally considered delusional. These factors have led the psychiatrist Anthony David to note that "there is no acceptable (rather than accepted) definition of a delusion." In practice, psychiatrists tend to diagnose a belief as delusional if it is either patently bizarre, causing significant distress, or excessively pre-occupying the patient, especially if the person is subsequently unswayed in belief by counter-evidence or reasonable arguments.

It is important to distinguish true delusions from other symptoms such as anxiety, fear, or paranoia. To diagnose delusions a mental state examination may be used. This test includes appearance, mood, affect, behavior, rate and continuity of speech, evidence of hallucinations or abnormal beliefs, thought content, orientation to time, place and person, attention and concentration, insight and judgment, as well as short-term memory.

Johnson-Laird suggests that delusions may be viewed as the natural consequence of failure to distinguish conceptual relevance. That is, the person takes irrelevant information and puts it in the form of disconnected experiences, then it is taken to be relevant in a manner that suggests false causal connections. Furthermore, the person takes the relevant information, in the form of counterexamples, and ignores it.

Some critical psychiatrists criticize the practice of defining one and the same belief as normal in one culture and pathological in another culture for cultural essentialism. They argue that since cultural influences are mixed, including not only parents and teachers but also peers, friends, books and the internet, and the same cultural influence can have different effects depending on earlier cultural influences, the assumption that culture can be boiled down to a few traceable, distinguishable and statistically quantifiable factors and that everything that does not fall in those factors must be biological, is not a justified assumption. Other critical psychiatrists argue that just because a person's belief is unshaken by one influence does not prove that it would remain unshaken by another. For example, a person whose beliefs are not changed by verbal correction from a psychiatrist, which is how delusion is usually diagnosed, may still change his or her mind when observing empirical evidence, only that psychiatry rarely if ever present patients with such situations.

Studies of borderline children often uncovered at the base of their self-destructive behaviour patterns ' a "fixed fantasy"...a rigid, nonreflective scenario of self-induced pain'. As part of a psychic defence mechanism, 'the omnipotence betrayed by the "fixed fantasy" underlying self-victimization or other forms of self-defeating behaviour...creates the illusory sense that they are actively producing the abandonment [&] pain', rather than merely suffering it passively - 'arranging deceits..arrang[ing] for blows to fall'. Unfortunately 'in the course of development, these patterns acquire multiple adaptive functions...and serve as a key organizer of their sense of self'.

'In producing movement away from fixed fantasy systems, commonplace statements are often necessary because the more fixed and extensive the fantasy system, the fewer the transitional opportunities offered; there is little conflicting material to ride. Banalities may be the only resource', as anything more complex may be used to feed back into the fantasy system itself.

In 2009 Amy Marsh, a clinical sexologist, surveyed the twenty-one English-speaking members of Erika Eiffel's 40-strong OS Internationale about their experiences. About half reported autism spectrum disorders: six had been diagnosed, four were affected but not diagnosed, and three of the remaining nine reported having "some traits." According to Marsh, "The emotions and experiences reported by OS people correspond to general definitions of sexual orientation," such as that in an APA article "on sexual orientation and homosexuality ... [which] refers to sexual orientation as involving 'feelings and self concept.'"

Object sexuality or objectophilia is a form of sexuality focused on particular inanimate objects. Those individuals with this expressed preference may feel strong feelings of attraction, love, and commitment to certain items or structures of their fixation. For some, sexual or even close emotional relationships with humans are incomprehensible. Some object-sexual individuals also often believe in animism, and sense reciprocation based on the belief that objects have souls, intelligence, and feelings, and are able to communicate.

A challenge in the treatment of delusional disorders is that most patients have limited insight, and do not acknowledge that there is a problem. Most patients are treated as out-patients, although hospitalization may be required in some cases if there is a risk of harm to self or others. Individual psychotherapy is recommended rather than group psychotherapy, as patients are often quite suspicious and sensitive. Antipsychotics are not well tested in delusional disorder, but they do not seem to work very well, and often have no effect on the core delusional belief. Antipsychotics may be more useful in managing agitation that can accompany delusional disorder. Until further evidence is found, it seems reasonable to offer treatments which have efficacy in other psychotic disorders.

Psychotherapy for patients with delusional disorder can include cognitive therapy which is conducted with the use of empathy. During the process, the therapist can ask hypothetical questions in a form of therapeutic Socratic questioning. This therapy has been mostly studied in patients with the persecutory type. The combination of pharmacotherapy with cognitive therapy integrates treating the possible underlying biological problems and decreasing the symptoms with psychotherapy as well. Psychotherapy has been said to be the most useful form of treatment because of the trust formed in a patient and therapist relationship.

Supportive therapy has also been shown to be helpful. Its goal is to facilitate treatment adherence and provide education about the illness and its treatment.

Furthermore, providing social skills training has helped many persons. It can promote interpersonal competence as well as confidence and comfort when interacting with those individuals perceived as a threat.

Insight-oriented therapy is rarely indicated or contraindicated; yet there are reports of successful treatment. Its goals are to develop therapeutic alliance, containment of projected feelings of hatred, impotence, and badness; measured interpretation as well as the development of a sense of creative doubt in the internal perception of the world. The latter requires empathy with the patient's defensive position.

The Gudjonsson Compliance Scale is a self-report instrument that measures peoples' levels of compliance. It focuses on two types of behavior, namely eagerness to please others, and avoidance of conflicts. The scale consists of 20 items using

a true/false format. Examples are 'I give in easily to people when I am pressured' and 'I try hard to do what is expected of me'. After recoding items 17 to 19, a total GCS score varying from 0 to 20 can be obtained by summing the number of true responses, with higher scores indexing more compliant behavior.

Individual therapy may be best suited to treat the individual's delusions. Persistence is needed in establishing a therapeutic empathy without validating the patient’s delusional system or overtly confronting the system. Cognitive techniques that include reality testing and reframing can be used. Antipsychotics and other therapeutic drugs have been used with relative success.

Aversion to happiness, also called cherophobia or fear of happiness, is an attitude towards happiness in which individuals may deliberately avoid experiences that invoke positive emotions or happiness.

One of several reasons that cherophobia may develop is the belief that when one becomes happy, a negative event will soon occur that will taint their happiness, as if that individual is being punished for satisfaction. This belief is thought to be more prevalent in non-Western cultures. In Western cultures, such as American culture, "it is almost taken for granted that happiness is one of the most important values guiding people’s lives." Western cultures are more driven by an urge to maximize happiness and minimize sadness. Failing to appear happy is often a cause for concern. Its value is echoed through Western positive psychology and research on subjective well-being.. Fear of happiness is associated with fragility of happiness beliefs, suggesting that one of the causes of aversion to happiness may be the belief that happiness is unstable and fragile . Fear of happiness has also been linked to avoidant and anxious attachment styles.

In Scientology, an implant is a form of Thought insertion, similar to an engram but done deliberately and with evil intent. It is "an intentional installation of fixed ideas, contra-survival to the thetan".

The intention in the original engram or incident is to implant an idea or emotion or sensation, regarding some phenomenon etc. The intention in Scientology and Dianetics is to erase the compulsive or command effect of the idea, emotion, sensation, etc. so that the person can make a rational judgment and decision in the affected areas of life.

Scientology practices often have to do with addressing implants prior to the current lifetime — one of the most notable is the "R6 implant"; but in some cases current life implants are addressed. Examples of implants according to Scientology include Aversion therapy, Electroconvulsive therapy, hypnosis, various attempts at brainwashing, and the inducing of fear or terror. Note that this is not a complete list, as many kinds of incidents can include implants as an element.

Other important implants in Scientology doctrine include the Helatrobus implants, which Hubbard claimed occurred 382 trillion years ago to 52 trillion years ago by an alien nation called the Helatrobans, who sought to restrain human minds by capturing and brainwashing thetans. These implants are said to be responsible for the concept of Heaven.

Delusions – fixed, fallacious beliefs – are symptoms that, in the absence of organic disease, indicate psychiatric disease. The content of delusions varies considerably (limited by the imagination of the delusional person), but certain themes have been identified; for example persecution. These themes have diagnostic importance in that they point to certain diagnoses. Persecutory delusions are, for instance, classically linked to psychosis.

Treatment of secondary forms of delusional parasitosis are addressed by treating the primary associated psychological or physical condition. The primary form is treated much as other delusional disorders and schizophrenia. In the past, pimozide was the drug of choice when selecting from the typical antipsychotics. Currently, atypical antipsychotics such as olanzapine or risperidone are used as first line treatment.

However, it is also characteristic that sufferers will reject the diagnosis of delusional parasitosis by medical professionals, and very few are willing to be treated, despite demonstrable efficacy of treatment.

The Gudjonsson suggestibility scale (GSS) is used to measure interrogative suggestibility. The GSS consists of a story that is read out loud by a test administer. Participants then have to answer 20 questions of which 15 are misleading and 5 are neutral and address factual details of the story. After participants have answered the questions, they receive negative feedback about their performance. They are asked to answer the questions one more time and to be more accurate this time. Thus, all questions are answered twice and in this way several GSS parameters can be calculated. First, yield 1 refers to the number of misleading questions that the participant accepts during the first round (range 0–15). Second, yield 2 refers to the number of misleading questions accepted during the second round (range 0–15). Third, shift refers to the number of changes that participants make in their answers after having received negative feedback (range 0–20). Finally, the total GSS score is the sum of yield 1 and shift, with higher scores reflecting higher levels of interrogative suggestibility (range 0–35).

In psychiatry, thought withdrawal is the delusional belief that thoughts have been 'taken out' of the patient's mind, and the patient has no power over this. It often accompanies thought blocking. The patient may experience a break in the flow of their thoughts, believing that the missing thoughts have been withdrawn from their mind by some outside agency. This delusion is one of Schneider's first rank symptoms for schizophrenia. Because thought withdrawal is characterized as a delusion, according to the DSM-IV TR it represents a positive symptom of schizophrenia.

Delusional misidentification syndrome is an umbrella term, introduced by Christodoulou (in his book "The Delusional Misidentification Syndromes", Karger, Basel, 1986) for a group of delusional disorders that occur in the context of mental and neurological illness. They all involve a belief that the identity of a person, object, or place has somehow changed or has been altered. As these delusions typically only concern one particular topic, they also fall under the category called monothematic delusions.

This psychopathological syndrome is usually considered to include four main variants:

- The Capgras delusion is the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor.

- The Fregoli delusion is the belief that various people the believer meets are actually the same person in disguise.

- Intermetamorphosis is the belief that people in the environment swap identities with each other whilst maintaining the same appearance.

- Subjective doubles, described by Christodoulou in 1978 ("American Journal of Psychiatry" 135, 249, 1978), is the belief that there is a doppelgänger or double of him- or herself carrying out independent actions.

However, similar delusional beliefs, often singularly or more rarely reported, are sometimes also considered to be part of the delusional misidentification syndrome. For example:

- Mirrored-self misidentification is the belief that one's reflection in a mirror is some other person.

- Reduplicative paramnesia is the belief that a familiar person, place, object, or body part has been duplicated. For example, a person may believe that they are in fact not in the hospital to which they were admitted, but an identical-looking hospital in a different part of the country, despite this being obviously false.

- The Cotard delusion is a rare disorder in which people hold a delusional belief that they are dead (either figuratively or literally), do not exist, are putrefying, or have lost their blood or internal organs. In rare instances, it can include delusions of immortality.

- Syndrome of delusional companions is the belief that objects (such as soft toys) are sentient beings.

- Clonal pluralization of the self, where a person believes there are multiple copies of him- or herself, identical both physically and psychologically but physically separate and distinct.

There is considerable evidence that disorders such as the Capgras or Fregoli syndromes are associated with disorders of face perception and recognition. However, it has been suggested that all misidentification problems exist on a continuum of anomalies of familiarity, from déjà vu at one end to the formation of delusional beliefs at the other.