• Hallucinations come in many forms including visual, auditory, and tactile. 
  • Hallucinations could be the result of a brain tumor, vision loss, or a degenerative disease.
  • Other causes include lack of sleep, medication side effects, infection, or illicit drug use.

A hallucination is when you see, hear, smell, taste or feel something that appears to be real but doesn't actually exist. For example, you might hear voices or see other people in the room who aren't there. 

The interesting bit is that many people who are hallucinating don't know what's actually happening. So, how do you differentiate reality from illusion?

"Ask somebody else, are they seeing this, or are they hearing that?" says Sarah Keedy, an associate professor of psychiatry and behavioral neuroscience at the University of Chicago. "If you're the only one, that's probably a hallucination."

There are many different causes of hallucinations, ranging from psychiatric disorders to hallucinogenic drugs. 

Generally speaking, if you are hallucinating and have not recently taken a psychoactive substance, you should consult a doctor who can identify the underlying cause and discuss treatment options, Keedy says. 

Here are some of the most common causes of hallucinations and how they're treated.

1. Lack of sleep

Although studies on sleep deprivation are no longer considered ethical, one 2018 review looked at 21 past studies completed before current medical ethics were established. 

This review found that minor illusions began as soon as 24 hours without sleep and progressed to more extreme hallucinations after two to four days. The most common type of hallucinations were visual hallucinations or distortions, such as: 

  • Imagining unknown objects sprouting from the floor
  • Seeing people in the room who were not present
  • Objects changing in color
  • Seeing more than one of an object

What to do about it: If you're experiencing hallucinations due to lack of sleep, the best thing to do is go to bed asap, says Dr. Kathleen M. Shannon, the chair of the Department of Neurology at the University of Wisconsin School of Medicine and Public Health.

However, various conditions, including insomnia, narcolepsy, aging, and chronic pain, can make it more difficult to sleep at night. If you are struggling to get to sleep because of an underlying medical condition, talk to a doctor who can recommend therapy, lifestyle changes, and in some cases medication to help you sleep.

2. Brain tumor

When brain tumors grow, they can put pressure on the brain, which may trigger visual, auditory, or other types of hallucinations depending on where the tumor is located in the brain.

For instance, if a tumor is aggravating the occipital lobe, which controls your vision, it can cause visual hallucinations that may persist for years, so long as the brain tumor remains. 

Now, chances are what's causing your hallucinations is not a brain tumor, since they affect about 0.03% of the US adult population. 

But if you're worried it may be a brain tumor, some other symptoms include:

  • Headaches
  • Seizures
  • Difficulty thinking or speaking
  • Memory loss
  • Personality changes
  • Loss of hearing or vision

What to do about it: If you think you have a brain tumor, a doctor will likely schedule you for some brain scans followed by a biopsy, if the scans identify something. 

Depending on the type and size of the tumor, a doctor may suggest surgical removal, radiation therapy, chemotherapy, or some combination of the three. 

3. Charles Bonnet syndrome

Charles Bonnet syndrome describes a series of visual hallucinations that people experience when they start to lose their vision. 

When a person is no longer able to see everything they used to, their brain sometimes responds by generating spontaneous visions, Shannon says. These can include visual hallucinations.

These hallucinations can be elaborate visions, like people or landscapes, or they can be simple flashes of light and colors. 

Charles Bonnet syndrome doesn't affect everyone with vision loss, but is surprisingly common among people with age-related macular degeneration, affecting 12% according to a 2021 study.

Most people with Charles Bonnet syndrome understand that they are hallucinating and experience little to no other symptoms, aside from vision loss. But even if you know what you see isn't real, hallucinations can be alarming.

What to do about it: There is no treatment for the condition, but you can reduce the negative impact hallucinations may have on your life with management techniques, such as attending support groups or doing eye exercises when you are hallucinating.

4. Infection

You may also experience hallucinations if you're very sick with an infection or fever. These hallucinations are a symptom of delirium, Shannon says, a disruption in your ability to think and interact with the world normally. 

If you have delirium, you are most likely to experience visual hallucinations, though other types of hallucinations, like auditory or tactile hallucinations, are also possible.

"We categorize these people [with delirium] as having what's called metabolic encephalopathy, which means sick brain, basically," Shannon says. Metabolic encephalopathy can result from a lack of oxygen, high fever, toxin, or anything else that disrupts the normal functioning of the brain. Because the brain requires so much energy to work normally, anything that disturbs it can cause acute confusion and delirium-associated hallucinations.

Some infections which can lead to hallucinations include:

People who have recently had major surgeries, including heart surgeries, can also experience hallucinations.

What to do about it: Most patients who are sick enough to hallucinate are already hospitalized, Shannon says. 

However, if you're not in a hospital or other medical institution, and you're experiencing a fever over 103 °F or infection significant enough to cause a hallucination, you should seek medical aid immediately.

Bacterial infections, like sepsis and UTIs, are treated with antibiotics. Viral infections like HSE  can sometimes be treated with antivirals like Aciclovir, though these are most effective if administered within the first few days of symptoms. 

5. Degenerative disease

Some degenerative diseases, including Alzheimer's disease, Parkinson's disease, and Lewy Body Dementia, can also cause hallucinations. 

The types of hallucinations depend on the degenerative disease in question: 

  • Alzheimer's: Visual and auditory hallucinations are the most common type and can include phenomena like patients believing a child is in the room with them when they are not.
  • Dementia with Lewy Bodies (LBD): Patients usually experience visual hallucinations early in the onset of their disease.
  • Parkinson's disease can cause visual hallucinations that typically develop later on, after a person has been sick for at least five years, Shannon says. Moreover, dopamine treatments for Parkinson's may also cause hallucinatory side effects.

Other symptoms of these degenerative diseases include:

Alzheimer's disease

Lewy Body Dementia

Parkinson's disease

Memory impairment

Changes in attention

Tremor

A hard time concentrating

Difficulty thinking

Slowed movement

Problems finishing daily tasks

Muscle stiffness or rigidity

Rigid muscles

Confusion

Tremor or shaking

Stooped posture

Older individuals are most at risk for developing these degenerative neurological conditions, but anyone is susceptible. 

What to do about it: Medications can sometimes be used to treat degenerative diseases. But lifestyle interventions are also key. 

For example, Alzheimer's patients may benefit from a regular schedule and having a trackable phone in case they get lost. 

For patients with Parkinson's and LBD patients, physical therapy can help patients stay strong and can reduce or delay the onset of physical symptoms.

6. Mental illness

Conditions like schizophrenia, bipolar disorder, and post-traumatic stress disorder (PTSD) can all cause hallucinations, most commonly auditory hallucinations like hearing voices. 

While these mental illnesses have a genetic component, some also have environmental triggers, like a traumatic event for PTSD, or stress for schizophrenia.

Aside from hallucinations, other symptoms may include the following:

  • Delusions and incoherent speech for schizophrenia
  • Periods of mania (such as high energy or confidence) alternating with periods of depression (such as sad mood or fatigue) for bipolar disorder
  • Intrusive memories and flashbacks for PTSD

What to do about it: Psychiatric disorders can be treated with medications like antipsychotics. While medication alone may not end the hallucinations, it can reduce other symptoms. 

Therapy can also help. "There are cognitive behavioral psychotherapies that can help people, not necessarily help the symptoms go away, but can help you live more effectively with it and it can help reduce the severity and the stress you experience," Keedy says.

7. Medications

The most common medications that cause hallucinations as a side effect are those for Parkinson's disease, such as Levodopa and carbidopa, Shannon says. 

But there are other medications that can also cause hallucinations, though this side effect is rare. Some of these drugs include:

What to do about it: There's not much you can do to prevent negative side effects from taking a drug, Keedy says. If you're worried that your medication may be causing hallucinations, you should call your prescribing physician. But don't quit taking the medicine cold turkey. 

"I would never advise to stop a medication on your own decision," Keedy says. "You should consult with a physician when you want to stop any medication they provide to you for any reason."

8. Illicit drugs

Illicit drugs and substances, such as LSD, psilocybin, peyote, ketamine, or PCP, can all trigger a range of hallucinations, visual illusions being the most common. 

For instance, if you ingest LSD, you might experience visual distortions of color and hallucinate the presence of creatures like fairies.

Typically, people who take an illicit psychoactive drug are prepped and ready for the hallucinations that follow. However, these hallucinations can be extremely vivid and may become overwhelming. 

What to do about it: Unfortunately, if you're having a bad trip, there's not much you can do except wait for your system to metabolize the drugs. 

Here's how long the effects of some common psychoactive drugs last:

However, if you are extremely and severely distressed, you can visit an emergency room for professional support, Keedy says.

"If a person is really agitated, we can give them sedatives to calm them down," says Dr. Stephan Taylor, a professor of psychiatry at the University of Michigan Ann Arbor who runs its PREP Early Psychosis Clinic. "Sometimes those can also stop the hallucinations."

When to see a doctor

If you are experiencing hallucinations and are not sure as to the cause, you should go see a physician.

Moreover, seek medical aid if your hallucinations are accompanied by a fever or illness, or if you are experiencing other psychiatric symptoms. 

A doctor may conduct a brain scan or blood test to check for any physical causes before examining you for a potential psychiatric disorder. 

Insider's takeaway

Hallucinations can indicate the presence of a serious neurological or psychiatric condition. If you are experiencing hallucinations, be sure to check in with a doctor. 

Don't assume that hallucinations are necessarily a sign of psychiatric disorder. 

"Hallucinations are almost always attributed to psychiatric disease by the general population," says Shannon. "So it's important to understand that these can be a manifestation of neurologic disease or a neurologic effect of another disease."

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