Psychosis vs. Delirium: How Medical Illness and Metabolic Shifts Can Trigger Acute Hallucinations

Seeing or hearing things that are not there can be frightening for the person experiencing it and for those around them. Hallucinations may occur in psychosis, delirium, medication reactions, substance use, severe sleep loss, or a range of medical and neurological conditions.

The most important distinction is that delirium is usually a sudden change in attention and awareness caused by an underlying medical problem, while psychosis is a group of symptoms involving a loss of contact with reality. The two can look similar, and they can occur together. A new episode of hallucinations, confusion, or unusual behavior should therefore be assessed by a healthcare professional rather than assumed to be a primary psychiatric illness.

What is psychosis?

Psychosis is a syndrome—not a single diagnosis. It affects how a person interprets reality and may involve:

• Hallucinations: hearing, seeing, feeling, smelling, or tasting something that is not actually present
• Delusions: strongly held beliefs that are not supported by evidence, such as believing someone is secretly monitoring the person
• Disorganized thinking or speech: difficulty connecting ideas or communicating clearly
• Markedly disorganized behavior: unusual actions, agitation, or behavior that seems out of context
• Reduced emotional expression or withdrawal in some cases

Psychosis can occur in conditions such as schizophrenia, bipolar disorder, severe depression, and postpartum psychiatric illness. It may also be triggered by sleep deprivation, recreational drugs, medication effects, seizures, brain disease, infections, or metabolic disturbances.

A person with psychosis may be awake and able to focus reasonably well, even though their beliefs or perceptions are inaccurate. However, attention and awareness can become impaired, especially when psychosis is caused by a medical condition or substance.

What is delirium?

Delirium is a rapid change in mental function. Its defining feature is impaired attention—the ability to focus, shift, and sustain attention—along with a change in awareness and thinking.

Typical features include:

• A sudden onset over hours or days
• Symptoms that fluctuate, often becoming worse at night
• Difficulty following a conversation or staying focused
• Disorientation about time, place, or situation
• Rambling, unclear, or unusually slow speech
• Changes in the sleep–wake cycle
• Agitation, drowsiness, or alternating between the two
• Hallucinations, often visual, although other types can occur

Delirium is common in older adults, people in hospital, and those with serious illness, but it can affect anyone if the underlying trigger is severe enough. It is not simply “being confused.” Delirium can signal a potentially urgent medical problem.

Psychosis vs. delirium: the key differences

The distinction is not always obvious, but several patterns are helpful:

Feature	Psychosis	Delirium
Onset	May develop gradually or suddenly	Usually sudden, over hours to days
Attention	Often relatively preserved	Clearly impaired
Awareness	Usually more stable	Fluctuates during the day
Orientation	May be intact	Often impaired
Hallucinations	Auditory hallucinations are common	Visual hallucinations are common, but any type may occur
Cause	Psychiatric illness, substances, medicines, or medical disease	Usually an acute medical, medication, or substance-related problem
Course	May persist without treatment	Often changes rapidly and improves when the cause is treated

These are general patterns, not rules. A person can have a psychiatric disorder and delirium at the same time. For example, someone with a history of bipolar disorder may develop delirium from pneumonia or a severe metabolic imbalance.

How medical illness can trigger hallucinations

The brain depends on a stable supply of oxygen, glucose, electrolytes, hormones, and other chemicals. When illness disrupts these conditions, brain function can change quickly.

Potential medical triggers include:

• Infections, including urinary, lung, bloodstream, or brain infections
• Low oxygen levels, severe breathing problems, or heart failure
• Low blood sugar, especially in people treated for diabetes
• Very high blood sugar and diabetic emergencies
• Sodium, calcium, or other electrolyte abnormalities
• Kidney or liver failure, which can allow waste products to build up
• Thyroid or adrenal disorders
• Stroke, seizures, head injury, or other neurological disease
• Vitamin deficiencies, particularly severe thiamine deficiency
• High fever, dehydration, severe pain, or prolonged sleep deprivation

A medical trigger can produce hallucinations without causing a long-term psychiatric condition. Treating the infection, correcting the metabolic problem, restoring oxygen, or addressing another underlying cause may allow the person’s thinking to return to normal.

Medications and substances

Both prescribed and nonprescription substances can contribute to psychosis or delirium. Examples include:

• Steroids such as prednisone
• Some medicines for pain, sleep, allergies, or Parkinson’s disease
• Anticholinergic medications, which can cause confusion and dry mouth
• Certain seizure or psychiatric medications
• Alcohol or sedative withdrawal
• Stimulants such as amphetamines or cocaine
• Hallucinogens and other recreational drugs
• Medication interactions or accidental overdose

A sudden change after starting, stopping, or increasing a medication is important information. Do not stop a prescribed medicine abruptly unless a clinician tells you to. Instead, contact a doctor, pharmacist, or urgent care service for guidance.

Why delirium should be taken seriously

Delirium is often a sign that the body or brain is under significant stress. The treatment is not simply to calm the person; clinicians need to identify and correct the cause. Evaluation may include a physical and neurological examination, medication review, blood and urine tests, blood glucose and oxygen checks, and sometimes brain imaging or other testing.

Families can help by:

• Speaking calmly and using short, reassuring sentences
• Reminding the person where they are and who is present
• Making sure glasses and hearing aids are available
• Supporting regular sleep and gentle daytime activity
• Reducing unnecessary noise and bright light at night
• Avoiding arguments about hallucinations; acknowledge that the experience feels real without confirming the belief
• Telling clinicians about recent illness, falls, medication changes, alcohol use, and the person’s usual mental state

When to seek urgent help

Seek emergency medical care for new hallucinations or confusion when they occur with:

• Difficulty breathing, chest pain, fainting, or severe weakness
• A seizure, severe headache, head injury, or one-sided weakness
• High fever, stiff neck, or a rapidly worsening condition
• Very low or high blood sugar
• Extreme agitation, dangerous behavior, or inability to stay safe
• Severe alcohol or sedative withdrawal
• Thoughts of suicide, harm to others, or inability to meet basic needs
• Sudden confusion in an older adult or someone with a serious medical condition

Even without these warning signs, a first episode of psychosis, delirium, or unexplained hallucinations should be discussed promptly with a doctor. Speak to a doctor about anything that could be life-threatening or serious. If immediate danger is present, contact local emergency services rather than relying on an online tool.

For general guidance while deciding what to do next, you might consider a free, online symptom check, using the doctor approved Ubie Symptom Checker. It cannot diagnose psychosis, delirium, or an underlying medical emergency, and it should not delay urgent care.

The central message is simple: sudden hallucinations are not always a psychiatric problem. Psychosis and delirium overlap, but delirium’s rapid onset, impaired attention, and fluctuating awareness often point to an acute medical or substance-related cause. Prompt assessment gives clinicians the best chance of finding that cause and treating it safely.