They are normally colorful, vivid images and occur during wakefulness, and predominately at night. Lilliputian hallucinations (also called Alice in Wonderland syndrome), hallucinations in which people or animals appear smaller than they would be in real life, are common in cases of peduncular hallucinosis. Most patients exhibit abnormal sleep patterns characterized by insomnia and daytime drowsiness. Peduncular hallucinosis has been described as a “release phenomenon” due to damage to the ascending reticular activating system, which is supported by the sleep disturbance characteristic of this syndrome. In most cases, people are aware that the hallucinations are not real. However, some people experience agitation and delusion and mistake their hallucinations for reality.

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.

Charles Bonnet syndrome is the name given to visual hallucinations experienced by a partially or severely sight impaired person. The hallucinations can occur at any time and can distress people of any age, as they may not initially be aware that they are hallucinating, they may fear initially for their own mental health which may delay them sharing with carers what is happening until they start to understand it themselves. The hallucinations can frighten and disconcert as to what is real and what is not and carers need to learn how to support sufferers. The hallucinations can sometimes be dispersed by eye movements, or perhaps just reasoned logic such as, "I can see fire but there is no smoke and there is no heat from it" or perhaps "We have an infestation of rats but they have pink ribbons with a bell tied on their necks." Over elapsed months and years the manifestation of the hallucinations may change, becoming more or less frequent with changes in ability to see. The length of time that the sight impaired person can suffer from these hallucinations varies according to the underlying speed of eye deterioration. A differential diagnosis are ophthalmopathic hallucinations.

This type of hallucination is usually experienced during the recovery from a comatose state. The migraine coma can last for up to two days, and a state of depression is sometimes comorbid. The hallucinations occur during states of full consciousness, and insight into the hallucinatory nature of the images is preserved. It has been noted that ataxic lesions accompany the migraine coma.

According to the DSM-IV-TR diagnostic criteria for delusional disorders, grandiose-type symptoms include grossly exaggerated beliefs of:

- self-worth

- power

- knowledge

- identity

- exceptional relationship to a divinity or famous person.

For example, a patient who has fictitious beliefs about his or her power or authority may believe himself or herself to be a ruling monarch who deserves to be treated like royalty.

There are substantial differences in the degree of grandiosity linked with grandiose delusions in different patients. Some patients believe they are God, the Queen of England, a president's son, a famous rock star, and so on. Others are not as expansive and think they are skilled sports-persons or great inventors.

Expansive delusions may be maintained by auditory hallucinations, which advise the patient that they are significant, or confabulations, when, for example, the patient gives a thorough description of their coronation or marriage to the king. Grandiose and expansive delusions may also be part of fantastic hallucinosis in which all forms of hallucinations occur.

Both alcoholic hallucinosis and DTs have been thought of as different manifestations of the same physiological process in the body during alcohol withdrawal. Alcoholic hallucinosis is a much less serious diagnosis than delirium tremens. Delirium tremens (DTs) do not appear suddenly, unlike alcoholic hallucinosis. DTs also take approximately 48 to 72 hours to appear after the heavy drinking stops. A tremor develops in the hands and can also affect the head and body. A common symptom of delirium tremens is that people become severely uncoordinated. The biggest difference between alcoholic hallucinosis and delirium tremens is that alcoholic hallucinosis have a much better prognosis than DTs. Moreover, delirium tremens can be fatal when untreated.

The cause of alcoholic hallucinosis is unclear. It seems to be highly related to the presence of dopamine in the limbic system with the possibility of other systems. There are many symptoms that could possibly occur before the hallucinations begin. Symptoms include headache, dizziness, irritability, insomnia, and indisposition. Typically, alcoholic hallucinosis has a sudden onset.

The main symptoms of delirium tremens are nightmares, agitation, global confusion, disorientation, visual and auditory hallucinations, tactile hallucinations, fever, high blood pressure, heavy sweating, and other signs of autonomic hyperactivity (fast heart rate and high blood pressure). These symptoms may appear suddenly, but typically develop two to three days after the stopping of heavy drinking, being worst on the fourth or fifth day. Also, these "symptoms are characteristically worse at night". In general, DT is considered the most severe manifestation of alcohol withdrawal and occurs 3–10 days following the last drink. Other common symptoms include intense perceptual disturbance such as visions of insects, snakes, or rats. These may be hallucinations, or illusions related to the environment, e.g., patterns on the wallpaper or in the peripheral vision that the patient falsely perceives as a resemblance to the morphology of an insect, and are also associated with tactile hallucinations such as sensations of something crawling on the subject—a phenomenon known as formication. Delirium tremens usually includes extremely intense feelings of "impending doom". Severe anxiety and feelings of imminent death are common DT symptoms.

DT can sometimes be associated with severe, uncontrollable tremors of the extremities and secondary symptoms such as anxiety, panic attacks and paranoia. Confusion is often noticeable to onlookers as those with DT will have trouble forming simple sentences or making basic logical calculations.

DT should be distinguished from alcoholic hallucinosis, the latter of which occurs in approximately 20% of hospitalized alcoholics and does not carry a significant mortality. In contrast, DT occurs in 5–10% of alcoholics and carries up to 15% mortality with treatment and up to 35% mortality without treatment. DT is characterized by the presence of altered sensorium; that is, a complete hallucination without any recognition of the real world. DT has extreme autonomic hyperactivity (high pulse, blood pressure, and rate of breathing), and 35-60% of patients have a fever. Some patients experience seizures.

Diagnosis is mainly based on symptoms. In a person with delirium tremens it is important to rule out other associated problems such as electrolyte abnormalities, pancreatitis, and alcoholic hepatitis.

A syndrome is a set of medical signs and symptoms occurring together, constitutes a particular disease or disorder. The word derives from the Greek σύνδρομον, meaning "concurrence". In some instances, a syndrome is so closely linked with a pathogenesis or cause that the words "syndrome", "disease", and "disorder" end up being used interchangeably for them. This is especially true of inherited syndromes. For example, Down syndrome, Wolf–Hirschhorn syndrome, and Andersen syndrome are disorders with known pathogeneses, so each is more than just a set of signs and symptoms, despite the "syndrome" nomenclature. In other instances, a syndrome is not specific to only one disease. For example, toxic shock syndrome can be caused by various toxins; premotor syndrome can be caused by various brain lesions; and premenstrual syndrome is not a disease but simply a set of symptoms.

If an underlying genetic cause is suspected but not known, a condition may be referred to as a genetic association (often just "association" in context). By definition, an association indicates that the collection of signs and symptoms occurs in combination more frequently than would be likely by chance alone.

Syndromes are often named after the physician or group of physicians that discovered them or initially described the full clinical picture. Such eponymous syndrome names are examples of medical eponyms. Recently, there has been a shift towards naming conditions descriptively (by symptoms or underlying cause) rather than eponymously, but the eponymous syndrome names often persist in common usage.

In medicine a broad definition of syndrome is used, which describes a collection of symptoms and findings without necessarily tying them to a single identifiable pathogenesis. The more specific definition employed in medical genetics describes a subset of all medical syndromes.

"Seeing pink elephants" is a euphemism for drunken hallucination caused by alcoholic hallucinosis or delirium tremens. The term dates back to at least the early 20th century, emerging from earlier idioms about snakes and other creatures. An alcoholic character in Jack London's 1913 novel "John Barleycorn" is said to hallucinate "blue mice and pink elephants".

A person with MS can have almost any neurological symptom or sign, with autonomic, visual, motor, and sensory problems being the most common. The specific symptoms are determined by the locations of the lesions within the nervous system, and may include loss of sensitivity or changes in sensation such as tingling, pins and needles or numbness, muscle weakness, blurred vision, very pronounced reflexes, muscle spasms, or difficulty in moving; difficulties with coordination and balance (ataxia); problems with speech or swallowing, visual problems (nystagmus, optic neuritis or double vision), feeling tired, acute or chronic pain, and bladder and bowel difficulties, among others. Difficulties thinking and emotional problems such as depression or unstable mood are also common. Uhthoff's phenomenon, a worsening of symptoms due to exposure to higher than usual temperatures, and Lhermitte's sign, an electrical sensation that runs down the back when bending the neck, are particularly characteristic of MS. The main measure of disability and severity is the expanded disability status scale (EDSS), with other measures such as the multiple sclerosis functional composite being increasingly used in research.

The condition begins in 85% of cases as a clinically isolated syndrome (CIS) over a number of days with 45% having motor or sensory problems, 20% having optic neuritis, and 10% having symptoms related to brainstem dysfunction, while the remaining 25% have more than one of the previous difficulties. The course of symptoms occurs in two main patterns initially: either as episodes of sudden worsening that last a few days to months (called relapses, exacerbations, bouts, attacks, or flare-ups) followed by improvement (85% of cases) or as a gradual worsening over time without periods of recovery (10–15% of cases). A combination of these two patterns may also occur or people may start in a relapsing and remitting course that then becomes progressive later on. Relapses are usually not predictable, occurring without warning. Exacerbations rarely occur more frequently than twice per year. Some relapses, however, are preceded by common triggers and they occur more frequently during spring and summer. Similarly, viral infections such as the common cold, influenza, or gastroenteritis increase their risk. Stress may also trigger an attack. Women with MS who become pregnant experience fewer relapses; however, during the first months after delivery the risk increases. Overall, pregnancy does not seem to influence long-term disability. Many events have been found not to affect relapse rates including vaccination, breast feeding, physical trauma, and Uhthoff's phenomenon.

Typically the severity of the symptoms experienced will depend on the amount and duration of prior alcohol consumption, as well as the number and severity of previous withdrawals. Even the most severe of these symptoms can occur in as little as 2 hours after cessation; therefore, the overall unpredictability necessitates either pre-planned hospitalization, treatment coordinated with a doctor, or at the very least rapid access to medical care, and a supporting system of friends or family should be introduced prior to addressing detoxification. In many cases, however, symptoms follow a reasonably predictable time frame as exampled below:

Six to 12 hours after the ingestion of the last drink, withdrawal symptoms such as shaking, headache, sweating, anxiety, nausea or vomiting occur. Other comparable symptoms may also exist in this period. Twelve to 24 hours after cessation, the condition may progress to such major symptoms as confusion, hallucinations (with awareness of reality), tremor, agitation, and similar ailments.

At 24 to 48 hours following the last ethanol ingestion, the possibility of seizures should be anticipated. Meanwhile, none of the earlier withdrawal symptoms will have abated. Seizures carry the risk of death for the alcoholic.

Although, most often, the patient's condition begins to improve past the 48-hour mark, it can sometimes continue to increase in severity to delirium tremens, characterized by hallucinations that are indistinguishable from reality, severe confusion, more seizures, high blood pressure and fever which can persist anywhere from 4 to 12 days.

Signs and symptoms of alcohol withdrawal occur primarily in the central nervous system. The severity of withdrawal can vary from mild symptoms such as sleep disturbances and anxiety to severe and life-threatening symptoms such as delirium, hallucinations, and autonomic instability.

Withdrawal usually begins 6 to 24 hours after the last drink. It can last for up to one week. To be classified as alcohol withdrawal syndrome, patients must exhibit at least two of the following symptoms: increased hand tremor, insomnia, nausea or vomiting, transient hallucinations (auditory, visual or tactile), psychomotor agitation, anxiety, tonic-clonic seizures, and autonomic instability.

The severity of symptoms is dictated by a number of factors, the most important of which are degree of alcohol intake, length of time the individual has been using alcohol, and previous history of alcohol withdrawal. Symptoms are also grouped together and classified:

- Alcohol hallucinosis: patients have transient visual, auditory, or tactile hallucinations, but are otherwise clear.

- Withdrawal seizures: seizures occur within 48 hours of alcohol cessations and occur either as a single generalized tonic-clonic seizure or as a brief episode of multiple seizures.

- Delirium tremens: hyperadrenergic state, disorientation, tremors, diaphoresis, impaired attention/consciousness, and visual and auditory hallucinations. This usually occurs 24 to 72 hours after alcohol cessation. Delirium tremens is the most severe form of withdrawal and occurs in 5 to 20% of patients experiencing detoxification and 1/3 of patients experiencing withdrawal seizures.

Symptoms vary depending on whether the spinal cord, brain stem, nerves or their blood supply is affected by the pressure.

Symptoms become apparent when the neck is bent. They include:

- Posterior head pain

- Neck weakness

- Periods of confusion

- Dysarthria (difficulty swallowing or talking due to loss of muscle control)

- Dizziness

- Loss of sensation

- Cranial nerve disturbance

- Loss of the ability to know how joints are positioned

- Lhermitte's sign ('electric shock sensation' down spine and/or to the extremities when the neck is flexed forward)

- Weakness of the arms and legs

- Orthostatic hypotension

- Patients will go into a pool and notice that below their belly button the water is not as cold as it is above.

Complications from this can include hydrocephalus, pseudotumor cerebri or syringomyelia because it blocks the flow of fluid around the brain and spinal cord.

Several phenotypes (commonly termed "types"), or patterns of progression, have been described. Phenotypes use the past course of the disease in an attempt to predict the future course. They are important not only for prognosis but also for treatment decisions. Currently, the United States National Multiple Sclerosis Society and the Multiple Sclerosis International Federation, describes four types of MS (revised in 2013):

1. Clinically isolated syndrome (CIS)

2. Relapsing-remitting MS (RRMS)

3. Primary progressive MS (PPMS)

4. Secondary progressive MS (SPMS)

Relapsing-remitting MS is characterized by unpredictable relapses followed by periods of months to years of relative quiet (remission) with no new signs of disease activity. Deficits that occur during attacks may either resolve or leave problems, the latter in about 40% of attacks and being more common the longer a person has had the disease. This describes the initial course of 80% of individuals with MS. When deficits always resolve between attacks, this is sometimes referred to as "benign MS", although people will still build up some degree of disability in the long term. On the other hand, the term "malignant multiple sclerosis" is used to describe people with MS having reached significant level of disability in a short period. The relapsing-remitting subtype usually begins with a clinically isolated syndrome (CIS). In CIS, a person has an attack suggestive of demyelination, but does not fulfill the criteria for multiple sclerosis. 30 to 70% of persons experiencing CIS later develop MS.

Primary progressive MS occurs in approximately 10–20% of individuals, with no remission after the initial symptoms. It is characterized by progression of disability from onset, with no, or only occasional and minor, remissions and improvements. The usual age of onset for the primary progressive subtype is later than of the relapsing-remitting subtype. It is similar to the age that secondary progressive usually begins in relapsing-remitting MS, around 40 years of age.

Secondary progressive MS occurs in around 65% of those with initial relapsing-remitting MS, who eventually have progressive neurologic decline between acute attacks without any definite periods of remission. Occasional relapses and minor remissions may appear. The most common length of time between disease onset and conversion from relapsing-remitting to secondary progressive MS is 19 years.

Other, unusual types of MS have been described; these include Devic's disease, Balo concentric sclerosis, Schilder's diffuse sclerosis, and Marburg multiple sclerosis. There is debate on whether they are MS variants or different diseases. Multiple sclerosis behaves differently in children, taking more time to reach the progressive stage. Nevertheless, they still reach it at a lower average age than adults usually do.

Acroparesthesia is severe pain in the extremities, and may be caused by Fabry disease, a type of sphingolipidosis.

It can also be a sign of hypocalcemia.

Paresthesia is an abnormal sensation such as tingling, tickling, pricking, numbness or burning of a person's skin with no apparent physical cause. The manifestation of a paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes.

The most familiar kind of paresthesia is the sensation known as "pins and needles" or of a limb "falling asleep". A less well-known and uncommon but important paresthesia is formication, the sensation of bugs crawling underneath the skin.

Basilar invagination is invagination (infolding) of the base of the skull that occurs when the top of the C2 vertebra migrates upward. It can cause narrowing of the foramen magnum (the opening in the skull where the spinal cord passes through to the brain). It also may press on the lower brainstem.

This is similar to Chiari malformation. That, however, is usually present at birth.

CCS is characterized by disproportionately greater motor impairment in upper compared to lower extremities, and variable degree of sensory loss below the level of injury in combination with bladder dysfunction and urinary retention. This syndrome differs from that of a complete lesion, which is characterized by total loss of all sensation and movement below the level of the injury.

In older patients, CCS most often occurs after acute hyperextension injury in an individual with long-standing cervical spondylosis. A slow, chronic cause in this age group is when the cord gets caught and squeezed between a posterior intervertebral disc herniation against the anterior cord and/or with posterior pressure on the cord from hypertrophy of the ligamentum flavum (Lhermitte's sign may be the experience that causes the patient to seek medical diagnosis). However, CCS is not exclusive to older patients as younger individuals can also sustain an injury leading to CCS. Typically, younger patients are more likely to get CCS as a result of a high-force trauma or a bony instability in the cervical spine. Historically, spinal cord damage was believed to originate from concussion or contusion of the cord with stasis of axoplasmic flow, causing edematous injury rather than destructive hematomyelia. More recently, autopsy studies have demonstrated that CCS may be caused by bleeding into the central part of the cord, portending less favorable prognosis. Studies also have shown from postmortem evaluation that CCS probably is associated with selective axonal disruption in the lateral columns at the level of the injury to the spinal cord with relative preservation of the grey matter.

The association between pink elephants and alcohol is reflected in the name of various alcoholic drinks. There are various cocktails called "Pink Elephant", and The Huyghe Brewery put a pink elephant on the label of its Delirium Tremens beer.

Symptoms suggestive of cord compression are back pain, a dermatome of increased sensation, paralysis of limbs below the level of compression, decreased sensation below the level of compression, urinary and fecal incontinence and/or urinary retention. Lhermitte's sign (intermittent shooting electrical sensation) and hyperreflexia may be present.