<unk><unk>  is commonly comorbid with other psychiatric illnesses, such as bipolar disorder or schizophrenia. The cause of the disorder is difficult to ascertain not only because of its rarity, but also due to the simultaneous presence of other disorders. While the physiological cause of the<unk>  has not been found, many hypotheses exist. Some researchers believe that the<unk>  appears as a symptom of another disorder instead of a disorder of its own. (see #Controversy, below) The<unk>  may also be related to substance dependence. Another hypothesis states that<unk><unk>  is result of hyper-identification, linked to over-activity in certain areas of the brain, thereby causing the patient see familiar aspects of the self in strangers. Cerebral hemispheres: Lesions in the right hemisphere, frontal lobes (pink), and temporal lobe(not shown) are linked to the<unk> . Some hypothesize that this delusion is a result of facial processing deficiencies, as it has seemingly similar symptoms of prosopagnosia; however, recognition of most faces is impaired in this delusion. Facial processing deficiencies also do not account for the occasion in which multiple<unk>  are reported. Another hypothesis is that a "disconnection" between the right and left hemispheres may cause the delusional symptoms. This hypothesis relies heavily on the theory of lateralization of brain function, or left brain vs. right brain theory. In this hypothesis, the inability of the right hemisphere to "check" the left hemisphere causes the individual to succumb to delusions of self-awareness created by the left hemisphere. Brain damage One hypothesis is that brain dysfunction (either due to physical damage or damage from an organic disorder) in the right hemisphere, temporal lobe, and/or bi-frontal lobes causes the delusion of<unk><unk> . Physical damage resulting in the<unk><unk>  delusion often includes, but is not limited to, brain lesions or traumatic brain injury. Suspected organic causes of brain damage that may lead to<unk><unk>  include disorders such as epilepsy. Because other mental illnesses are commonly co-morbid with<unk><unk>  syndrome, it is unknown whether these types of brain injuries are linked to the delusion or the additional mental illness. For example, right hemisphere brain damage is associated with schizophrenia, which is commonly reported with the delusion of<unk><unk> .
Syndrome of subjective doubles
Postorgasmic illness syndrome
Functional somatic syndrome
Paroxysmal extreme pain disorder
Vitreous touch syndrome
Nociplastic pain
Pseudobulbar affect
Feline hyperesthesia syndrome