Other olfactory disorders such as hyposmia and anosmia have been found to be a symptom of mood disorders (depression). However, it is not known what olfactory disorders occur and if they are indeed a symptom of a depressive disorder.

It has been found that phantosmia may be an early sign of the neurodegenerative disease Parkinson's disease. It may also be a sign of an intracranial hemorrhage (brain tumours or epilepsy).

Other studies have also found that the symptoms of phantosmia have been alleviated after the patient has been treated for depression.

Another case of a 70-year-old male reported that his first abnormal symptoms were irregular bowel movements. After this the patient developed irregular eye movements and had developed a sleep and behavior disorder after this he developed phantosmia; which was described to be as "stinky and unpleasant". The patient did not display the following symptoms: loss of awareness, confusion, automatisms, convulsive seizures, auditory/visual hallucinations.

The complaints of Phantosmia involving the perception of unpleasant odors most commonly include "burnt", "foul", "rotten", "sewage", "metallic" or "chemical". Sometimes the odor is described as exhaust fumes. These odors may be triggered by strong odorants, changes in nasal airflow, or even loud sounds; sometimes it occurs spontaneously. Patients having complaints of Phantosmia might self-admit a poor quality of life, with each meal having the unpleasant odor as well.

The disorder's first onset, usually spontaneous, lasts only a few minutes. Its recurrences are then gradually increased from monthly, then weekly, and then daily over a period of 6 months to a year. The duration of the perceived odor also increases over same time, often lasting most of a day after 1 year.

Some patients also state that the odor they smell is different from any known odor.

Parosmia (from the Greek παρά "pará" and ὀσμή "osmḗ"), also known as troposmia (Gk.) or cacosmia (Gk.), is an olfactory dysfunction that is characterized by the inability of the brain to properly identify an odor's "natural" smell.

What happens instead, is that the natural odor is transcribed into what is most often described as an unpleasant aroma, typically a "'burned,' 'rotting,' 'fecal,' or 'chemical' smell".

There are instances, however, of pleasant odors; this is more specifically called euosmia (Greek).

Olfactory dysfunction can be quantitative and/or qualitative. Quantitative smell disorders refer to disorders in which there is complete or partial loss of olfaction. Anosmia, the complete loss of olfaction, and hyposmia, the partial loss of olfaction are the two disorders classified as quantitative because they can be measured. Qualitative smell disorders can’t be measured and refer to disorders in which there is alternation or distortion in the perception of smell. Qualitative disorders include parosmia (also called troposmia) and phantosmia. The term dysosmia refers to a qualitative olfaction disorder and include both parosmia and phantosmia. Olfactory dysfunction including anosmia, hyposmia, and dysosmia can be either bilateral or unilateral on either nostril. Anosmia only on the left nostril would be termed unilateral left anosmia while bilateral anosmia would be termed total anosmia.

One method used to establish parosmia is the University of Pennsylvania Smell Identification Test, or UPSIT. "Sniffin' Sticks" are another method that can be used to properly diagnose parosmia. These different techniques can also help deduce whether a specific case of parosmia can be attributed to just one stimulating odor or if there is a group of stimulating odors that will generate the displaced smell. One case study performed by Frasnelli "et al." offers a situation where certain smells, specifically coffees, cigarettes, onions, and perfumes, induced a "nauseating" odor for the patient, one which was artificial but unable to be aptly related to another known smell. In another case study cited in the same paper, one woman had parosmia in one nostril but not the other. Medical examinations and MRIs did not reveal any abnormalities; however the parosmia in this case was degenerative and only got worse with time. The authors do comment, however, that cases of parosmia can predict regeneration of olfactory senses.

Parosmia refers to a distortion in the perception of an odorant. Odorants smell different from what one remembers. A more specific term, cacosmia, refers to an unpleasant perception of an odorant due to nasosinusal or pharyngeal infection.

Other visual hallucinations tend to stem from psychological disorders. Whereas a person with a psychological disorder thinks their hallucinations are real, people with peduncular hallucinosis normally know that the visual hallucinations they see are not real. Peduncular hallucinations are independent of seizures, unlike some other visual hallucinations.

Individuals with exploding head syndrome hear or experience loud imagined noises as they are falling asleep or waking up, have a strong, often frightened emotional reaction to the sound, and do not report significant pain; around 10% of people also experience visual disturbances like perceiving visual static, lightning, or flashes of light. Some people may also experience heat, strange feelings in their torso, or a feeling of electrical tinglings that ascends to the head before the auditory hallucinations occur. With the heightened arousal, people experience distress, confusion, myoclonic jerks, tachycardia, sweating, and the sensation that felt as if they had stopped breathing and had to make a deliberate effort to breathe again.

The pattern of the auditory hallucinations is variable. Some people report having a total of two or four attacks followed by a prolonged or total remission, having attacks over the course of a few weeks or months before the attacks spontaneously disappear, or the attacks may even recur irregularly every few days, weeks, or months for much of a lifetime.

Some individuals believe that EHS episodes are not natural events, but are the effects of directed energy weapons which create an auditory effect. Thus, EHS has been worked into conspiracy theories, but there is no scientific evidence that EHS has non-natural origins.

People diagnosed with Parkinson's disease, narcolepsy-cataplexy syndrome, delirium tremens, Lewy Body Dementia, and temporal lobe epilepsy are more prone to complex visual hallucinations such as peduncular hallucinosis. Peduncular hallucinosis is more common in patients with a long duration of Parkinson's disease and also with a long treatment history, depression, and cognitive impairment. Paranoid delusions are common in these patients even though the hallucinations can occur during clear sensorium.

Exploding head syndrome is classified as a parasomnia and a sleep-related dissociative disorder by the 2005 International Classification of Sleep Disorders and is an unusual type of auditory hallucination in that it occurs in people who are not fully awake.

The hallmark sign of Alice in Wonderland syndrome (AIWS) is a migraine, and AIWS may in part be caused by the migraine. AIWS affects the sense of vision, sensation, touch, and hearing, as well as one's own body image.

A prominent and often disturbing symptom are experiences of altered body image. The person may find that they are confused as to the size and shape of parts of (or all of) their body. They may feel as though their body is expanding or getting smaller. Alice in Wonderland syndrome also involves perceptual distortions of the size or shape of objects. Other possible causes and signs of the syndrome include migraines, use of hallucinogenic drugs, and infectious mononucleosis.

Patients with certain neurological diseases have experienced similar visual hallucinations. These hallucinations are called "Lilliputian," which means that objects appear either smaller or larger than they actually are.

Patients may experience either micropsia or macropsia. Micropsia is an abnormal visual condition, usually occurring in the context of visual hallucination, in which affected persons see objects as being smaller than those objects actually are. Macropsia is a condition where the individual sees everything larger than it actually is.

A relationship between the syndrome and mononucleosis has been suggested.

One 17-year-old male, Michael Huang, described his odd symptoms. He said, "quite suddenly objects appear small and distant (teliopsia) or large and close (peliopsia). I feel as I am getting shorter and smaller 'shrinking' and also the size of persons are not longer than my index finger (a lilliputian proportion). Sometimes I see the blind in the window or the television getting up and down, or my leg or arm is swinging. I may hear the voices of people quite loud and close or faint and far. Occasionally, I experience attacks of migrainous headache associated with eye redness, flashes of lights and a feeling of giddiness. I am always conscious to the intangible changes in myself and my environment."

The eyes themselves are normal, but the person will often 'see' objects as the incorrect size, shape or perspective angle. Therefore, people, cars, buildings, houses, animals, trees, environments, etc., look smaller or larger than they should be, or that distances look incorrect; for example, a corridor may appear to be very long, or the ground may appear too close.

The person affected by Alice in Wonderland Syndrome may also lose the sense of time, a problem similar to the lack of spatial perspective. In other words, time seems to pass very slowly, akin to an LSD experience. The lack of time, and space, perspective leads to a distorted sense of velocity. For example, one could be inching along ever so slowly in reality, yet it would seem as if one were sprinting uncontrollably along a moving walkway, leading to severe, overwhelming disorientation. This can then cause the person to feel as if movement, even within his or her own home, is futile.

In addition, some people may, in conjunction with a high fever, experience more intense and overt hallucinations, seeing things that are not there and misinterpreting events and situations.

Other minor or less common symptoms may include loss of limb control and general dis-coordination, memory loss, lingering touch and sound sensations, and emotional experiences.

Hallucinatory palinopsia consists of the following four symptom categories. A person often reports symptoms from multiple categories.

Anosmia is the inability to perceive odor or a lack of functioning olfaction—the loss of the sense of smell. Anosmia may be temporary, but some forms such as from an accident, can be permanent. Anosmia is due to a number of factors, including an inflammation of the nasal mucosa, blockage of nasal passages or a destruction of one temporal lobe. Inflammation is due to chronic mucosa changes in the paranasal sinus lining and the middle and superior turbinates.

When anosmia is caused by inflammatory changes in the nasal passageways, it is treated simply by reducing inflammation. It can be caused by chronic meningitis and neurosyphilis that would increase intracranial pressure over a long period of time, and in some cases by ciliopathy including ciliopathy due to primary ciliary dyskinesia (Kartagener syndrome, Afzelius' syndrome or Siewert's syndrome).

Many patients may experience unilateral anosmia, often as a result of minor head trauma. This type of anosmia is normally only detected if both of the nostrils are tested separately. Using this method of testing each nostril separately will often show a reduced or even completely absent sense of smell in either one nostril or both, something which is often not revealed if both nostrils are simultaneously tested.

A related term, hyposmia, refers to a decreased ability to smell, while hyperosmia refers to an increased ability to smell. Some people may be anosmic for one particular odor. This is known as "specific anosmia". The absence of the sense of smell from birth is called congenital anosmia.

Investigators have successfully narrowed down the major factors that are associated with musical hallucinations. Evers and Ellgers compiled a significant portion of musical hallucination articles, case studies etc. and were able to categorize five major etiologies:

- Hypoacusis

- Psychiatric disorders

- Focal brain lesion

- Epilepsy

- Intoxication

Anosmia can have a number of harmful effects. Patients with sudden onset anosmia may find food less appetizing, though congenital anosmics rarely complain about this, and none report a loss in weight. Loss of smell can also be dangerous because it hinders the detection of gas leaks, fire, and spoiled food. The common view of anosmia as trivial can make it more difficult for a patient to receive the same types of medical aid as someone who has lost other senses, such as hearing or sight.

Losing an established and sentimental smell memory (e.g. the smell of grass, of the grandparents' attic, of a particular book, of loved ones, or of oneself) has been known to cause feelings of depression.

Loss of olfaction may lead to the loss of libido, though this usually does not apply to congenital anosmics.

Often people who have congenital anosmia report that they pretended to be able to smell as children because they thought that smelling was something that older/mature people could do, or did not understand the concept of smelling but did not want to appear different from others. When children get older, they often realize and report to their parents that they do not actually possess a sense of smell, often to the surprise of their parents.

A study done on patients suffering from anosmia found that when testing both nostrils, there was no anosmia revealed; however, when testing each nostril individually, tests showed that the sense of smell was usually affected in only one of the nostrils as opposed to both. This demonstrated that unilateral anosmia is not uncommon in anosmia patients.

Hyperosmia is an increased olfactory acuity (heightened sense of smell), usually caused by a lower threshold for odor. This perceptual disorder arises when there is an abnormally increased signal at any point between the olfactory receptors and the olfactory cortex. The causes of hyperosmia may be genetic, environmental or the result of benzodiazepine withdrawal syndrome.

When odorants enter the nasal cavity, they bind to odorant receptors at the base of the olfactory epithelium. These receptors are bipolar neurons that connect to the glomerular layer of the olfactory bulb, traveling through the cribriform plate. At the glomerular layer, axons from the olfactory receptor neurons intermingle with dendrites from intrinsic olfactory bulb neurons: mitrial/tufted cells and dopaminergic periglomerular cells. From the olfactory bulb, mitral/tufted cells send axons via the lateral olfactory tract (the cranial nerve I) to the olfactory cortex, which includes the piriform cortex, entorhinal cortex, and parts of the amygdala. From the entorhinal cortex, axons extend to the medial dorsal nucleus of the thalamus, which then proceed to the orbitofrontal cortex.

Akinetic mutism can also occur as a result of damage to the mesencephalic region of the brain. Mesencephalic akinetic mutism is clinically categorized as somnolent or apathetic akinetic mutism. It is characterized by vertical gaze palsy and ophthalmoplegia. This state of akinetic mutism varies in intensity, but it is distinguished by drowsiness, lack of motivation, hyper-somnolence, and reduction in spontaneous verbal and motor actions.

In 73 individual cases reviewed by Evers and Ellger, 57 patients heard tunes that were familiar, while 5 heard unfamiliar tunes. These tunes ranged from religious pieces to childhood favorites, and also included popular songs from the radio. Vocal and instrumental forms of classical music were also identified in some patients. Keshavan found that the consistent feature of musical hallucinations was that it represented a personal memory trace. Memory traces refer to anything that may seem familiar to the patient, which indicated why certain childhood or familiar songs were heard.

Alice in Wonderland syndrome is a disturbance of perception rather than a specific physiological change to the body's systems. The diagnosis can be presumed when other causes have been ruled out and if the patient presents symptoms along with migraines and complains of onset during the day (although it can also occur at night).

Another symptom of Alice in Wonderland syndrome is sound distortion, such as every little movement making a clattering sound.

Akinetic mutism can occur in the frontal region of the brain and occurs because of bilateral frontal lobe damage. Akinetic mutism as a result of frontal lobe damage is clinically characterized as hyperpathic. It occurs in patients with bilateral circulatory disturbances in the supply area of the anterior cerebral artery.

Hallucinatory palinopsia (Greek: "palin" for "again" and "opsia" for "seeing") is a subtype of palinopsia, a visual disturbance defined as the persistent or recurrence of a visual image after the stimulus has been removed. Palinopsia is a broad term describing a heterogeneous group of symptoms which is divided into hallucinatory palinopsia and illusory palinopsia. Hallucinatory palinopsia refers to the projection of an already-encoded visual memory and is similar to a complex visual hallucination: the creation of a formed visual image where none exists.

Hallucinatory palinopsia usually arises from posterior cortical lesions or seizures and can be the presenting symptom of a serious neurological disease. Hallucinatory palinopsia describes afterimages or scenes that are formed, long-lasting, high resolution, and isochromatic. The palinoptic images are not typically reliant on environmental parameters and often present with homonymous visual field deficits. Hallucinatory palinopsia occurs unpredictably and the persistent images can appear anywhere in the visual field, regardless of the location of the original stimulus. A patient will often have only a few episodes of hallucinatory palinopsia. Visual perseveration is synonymous with palinopsia.

Tactile hallucination is the false perception of tactile sensory input that creates a hallucinatory sensation of physical contact with an imaginary object. It is caused by the faulty integration of the tactile sensory neural signals generated in the spinal cord and the thalamus and sent to the primary somatosensory cortex (SI) and secondary somatosensory cortex (SII). Tactile hallucinations are recurrent symptoms of neurological diseases such as schizophrenia, Parkinson's disease, Ekbom's syndrome and delerium tremens. Patients who experience phantom limb pains also experience a type of tactile hallucination. Tactile hallucinations are also caused by drugs such as cocaine and alcohol.

There has not been extensive research into environmental causes of hyperosmia, but there are some theories of some possible causes.

In a study by Atianjoh et al., it has been found that amphetamines decrease levels of dopamine in the olfactory bulbs of rodents. On this basis, it has been hypothesized that amphetamine use may cause hyperosmia in rodents and humans, but further research is still needed. Anecdotal support for the belief that amphetamines may cause hyperosmia comes from Oliver Sacks's account of a patient with a heightened sense of smell after taking amphetamines.

It has been observed that the inhalation of hydrocarbons can cause hyperosmia, most likely due to the destruction of dopaminergic neurons in the olfactory bulb.

Methotrexate, administered in the treatment of psoriasis, has been known to cause hyperosmia, and may be more likely to do so in patients with a history of migraines. However, this is only an observation and not part of a study, therefore it is yet to be verified.

Micropsia is the most common visual distortion, or dysmetropsia. It is categorized as an illusion in the positive phenomena grouping of abnormal visual distortions.

- Convergence-accommodative micropsia is a physiologic phenomenon in which an object appears smaller as it approaches the subject.

- Psychogenic micropsia can present itself in individuals with certain psychiatric disorders.

- Retinal micropsia is characterized by an increase in the distance between retinal photoreceptors and is associated with decreased visual acuity.

- Cerebral micropsia is a rare form of micropsia that can arise in children with chronic migraines.

- Hemimicropsia is a type of cerebral micropsia that occurs within one half of the visual field.

People with significant vision loss may have vivid, complex recurrent visual hallucinations (fictive visual percepts). One characteristic of these hallucinations is that they usually are "lilliputian" (hallucinations in which the characters or objects are smaller than normal). The most common hallucination is of faces or cartoons. Sufferers understand that the hallucinations are not real, and the hallucinations are only visual, that is, they do not occur in any other senses, e.g. hearing, smell or taste. Among older adults (> 65 years) with significant vision loss, the prevalence of Charles Bonnet syndrome has been reported to be between 10% and 40%; a 2008 Australian study found the prevalence to be 17.5%. Two Asian studies, however, report a much lower prevalence. The high incidence of non-reporting of this disorder is the greatest hindrance to determining the exact prevalence; non-reporting is thought to be a result of sufferers being afraid to discuss the symptoms out of fear that they will be labelled insane.

People suffering from CBS may experience a wide variety of hallucinations. Images of complex colored patterns and images of people are most common, followed by animals, plants or trees and inanimate objects. The hallucinations also often fit into the person's surroundings.