Oneirophenia and schizophrenia are often confused although there are distinct differences between the conditions. Oneirophrenia has some of the characteristics of simple schizophrenia, such as a confusional state and clouding of consciousness, but without presenting the dissociative symptoms which are typical of that disorder. Oneiophrenia often begins with the inability to focus on things while schizophrenia frequently starts with a traumatic event. Persons affected by oneirophrenia have a feeling of dream-like derealization which, in its extreme form, may progress to delusions and hallucinations. Therefore, it is considered a schizophrenia-like acute form of psychosis which remits in about 60% of cases within a period of two years. It is estimated that 50% or more of schizophrenic patients present oneirophrenia at least once.

Oneirophrenia is often described as a dream-like state that can lead to hallucinations and confusion. Feelings and emotions are often disturbed but information from the senses is left intact separating it from true schizophrenia.

Catatonia is a state of psycho-motor immobility and behavioral abnormality manifested by stupor. It was first described in 1874 by Karl Ludwig Kahlbaum, in ("Catatonia or Tension Insanity").

Though catatonia has historically been related to schizophrenia (catatonic schizophrenia), it is now known that catatonic symptoms are nonspecific and may be observed in other mental disorders and neurological conditions. In the fifth edition of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM), catatonia is not recognized as a separate disorder, but is associated with psychiatric conditions such as schizophrenia (catatonic type), bipolar disorder, post-traumatic stress disorder, depression and other mental disorders, narcolepsy, as well as drug abuse or overdose (or both). It may also be seen in many medical disorders including infections (such as encephalitis), autoimmune disorders, focal neurologic lesions (including strokes), metabolic disturbances, alcohol withdrawal and abrupt or overly rapid benzodiazepine withdrawal. In the fifth edition of the DSM, it is written that a variety of medical conditions may cause catatonia, especially neurological conditions: encephalitis, cerebrovascular disease, neoplasms, head injury. Moreover, metabolic conditions: homocystinuria, diabetic ketoacidosis, hepatic encephalopathy, hypercalcaemia.

It can be an adverse reaction to prescribed medication. It bears similarity to conditions such as encephalitis lethargica and neuroleptic malignant syndrome. There are a variety of treatments available; benzodiazepines are a first-line treatment strategy. Electroconvulsive therapy is also sometimes used. There is growing evidence for the effectiveness of NMDA receptor antagonists for benzodiazepine-resistant catatonia. Antipsychotics are sometimes employed but require caution as they can worsen symptoms and have serious adverse effects.

People with catatonia may experience an extreme loss of motor skill or even constant hyperactive motor activity. Catatonic patients will sometimes hold rigid poses for hours and will ignore any external stimuli. People with catatonic excitement can suffer from exhaustion if not treated. Patients may also show stereotyped, repetitive movements.

They may show specific types of movement such as waxy flexibility, in which they maintain positions after being placed in them by someone else. Conversely, they may remain in a fixed position by resisting movement in proportion to the force applied by the examiner. They may repeat meaningless phrases or speak only to repeat what the examiner says.

While catatonia is only identified as a symptom of schizophrenia in present psychiatric classifications, it is increasingly recognized as a syndrome with many faces. It appears as the Kahlbaum syndrome (motionless catatonia), malignant catatonia (neuroleptic malignant syndrome, toxic serotonin syndrome), and excited forms (delirious mania, catatonic excitement, oneirophrenia).

It has also been recognized as grafted on to autism spectrum disorders.

There are symptoms that are mechanism-based that are associated with hallucinations. These include superficial pressure and stabbing pain. Others include a burning-like sensation or electric shock feeling. Human studies of these symptoms remain mostly unclear unlike similar studies in animals.

Phantosmia (olfactory hallucinations), smelling an odor that is not actually there, and parosmia (olfactory illusions), inhaling a real odor but perceiving it as different scent than remembered, are distortions to the sense of smell (olfactory system) that, in most cases, are not caused by anything serious and usually go away on their own in time. It can result from a range of conditions such as nasal infections, nasal polyps, dental problems, migraines, head injuries, seizures, strokes, or brain tumors. Environmental exposures are sometimes the cause as well, such as smoking, exposure to certain types of chemicals (e.g., insecticides or solvents), or radiation treatment for head or neck cancer. It can also be a symptom of certain mental disorders such as depression, bipolar disorder, intoxication or withdrawal from drugs and alcohol, or psychotic disorders (e.g., schizophrenia). The perceived odors are usually unpleasant and commonly described as smelling burned, foul spoiled, or rotten.