Cristina Po Wenger
Author: Cristina Po Wenger Medical Reviewer: Dr. Brittany Ferri, PhD Last updated:

Delirium is the acute onset and temporary disturbances to a person’s consciousness, attention and awareness, often resulting in a debilitating state of sudden confusion.[1] Symptoms can vary depending on the type of delirium and can worsen if appropriate treatment isn’t given.

What is delirium?

Delirium (also called Acute Confusional State (ACS)) is a severe state of mental confusion and disorientation caused by a sudden change resulting in altered level of consciousness, cognition and perception, and inattention. In many cases, delirium causes a lack of awareness, so people may not understand that they have delirium. This can be distressing for the person experiencing an episode of delirium since it may cause anxiety related to disorientation and confusion.

Delirium is a syndrome comprised of several complex symptoms. Persistent delirium is typically misdiagnosed and mistreated as dementia, which is a separate cognitive disorder. They can share similar symptoms, but they are clinically very different. 

Depending on the type of delirium, a person experiencing an episode can present with psychotic features such as hallucinations, physical signs of stress like pacing, and behavioral changes such as aggressiveness.[2] Some severe cases of delirium will require emergency medical attention.

Types of delirium

There are three clinical subtypes of delirium categorized according to psychomotor activity and cause.

Hyperactive Delirium

  • A person with Hyperactive Delirium will display high energy along with psychomotor symptoms such as agitation, restlessness, rapid speech, hallucinations and rapid mood changes[3]
  • This particular delirium syndrome is easily recognized and is also the most life-threatening of all due to the high risk of unintentional injury (falling) and secondary physical trauma (being restrained)
  • Hyperactive delirium is a common complication in patients in Intensive Care Units (ICUs)

Hypoactive Delirium 

  • A person with Hypoactive Delirium will display low-energy symptoms like drowsiness, sluggishness, and slow speech. They may also experience a reduction in appetite
  • It is more difficult to recognize as it resembles depression, dementia, or generally poor motivation, which some patients may experience during long hospital stays.
  • Hypoactive delirium is the most common type in people with a terminal or critical illness 

Mixed Delirium

  • The person presents with/or shift between both symptoms of both hyper- and hypoactive delirium

Delirium Tremens 

  • Delirium Tremens (or Alcohol Withdrawal Delirium)differs entirely from the types of delirium outlined above. It is caused by alcohol withdrawal, but will resolve once the withdrawal period is over. However, it does require that the individual to be medically monitored for safety and to track their vital signs. [4]
  • A person presenting with this type of delirium will typically have, for example, tremors or shaking of the hands or feet, profuse sweating, hallucinations, dehydration, heightened body temperature and breathing, vomiting, heightened agitation
  • Delirium Tremens is most common in adult men who are heavy and long-term alcohol drinkers as well as those who have experienced alcohol withdrawals before

Symptoms of delirium

The onset of delirium occurs suddenly, meaning that the changes in a person’s physical and mental status can develop over hours or a few days. The severity of symptoms may fluctuate throughout the day and worsen in the evening (termed sundowning). However, sundowning is a type of delirium that almost exclusively impacts individuals with dementia.[3]

The following is a brief clinical description of the main delirium symptoms of hyperactive and hypoactive delirium and associated behaviors.

Altered Perception (Visual and Auditory)

A person with delirium may misinterpret their environment or the actions of those attending to them. As a result, the person may act aggressively.[3]

  • Paranoid delusions and illusions – firmly held false beliefs, misinterpreting the environment and surroundings 
  • Hallucinations – non-existent stimuli are perceived, such as hearing voices that aren’t there, seeing things that aren’t there, and feeling sensations on the skin that aren’t there

Cognitive Decline

Delirium can cause a person to experience sensory impairments in cognition and cognitive processes.

  • Language – impaired comprehension; incoherent; difficulty expressing themselves
  • Memory – limited short-term memory
  • Disorientated – disoriented to time, place, and person; disorganized thinking; illogical reasoning

Impairment of Consciousness 

A person with delirium can have significantly diminished awareness, attention and responsiveness to their environment.[2]

  • Inattentive – inability to focus on a topic; easily distracted; delayed response; unable to follow reasonable commands
  • Hyper-attentive – fixated on an idea or topic of their choosing, without being prompted about that topic
  • Sleep disturbances – reversal of the sleep-wake cycle; disturbances of the sleep-wake cycle (daytime drowsiness, night-time insomnia); excessive drowsiness

Emotional Disturbances 

Patients with delirium can display uncharacteristically extreme mood and emotional states – particularly in response to delusions or hallucinations.

For example:

  • Anger; combativeness; uncooperativeness
  • Elation; euphoria; hyper-vigilance 
  • Withdrawal; lethargy; apathy; depression
  • Agitation; anxiety; restlessness

In addition to these symptoms, people with delirium may also experience physical impairments such as dizziness, loss of coordination, falling down, and lightheadedness.

Diagnosing delirium

Doctors will conduct a preliminary evaluation of delirium from detailed historical medical records and informed observers (caregivers or family members). This procedure establishes a baseline of cognition and behaviors pre-onset. 

Clinical assessments for the detection of delirium include mental and physical examinations. The Confusion Assessment Method (CAM) is a widely used delirium assessment tool.[2] 

The Confusion Assessment Method assessment has four criteria: (1) Acute Onset and Fluctuation Course, (2) Inattention, (3) Disorganized Thinking and (4) Altered Levels of Consciousness. This assessment tool has variations developed to distinguish delirium from other types of cognitive impairment.[2] 

CAM scores are measured as (0) absent, (1) mild, (2) marked, and anything higher suggesting severe delirium. 

In addition, physical examinations in conjunction with assessment tools can be use to determine underlying causation. These can include checking blood pressure, heart rate, blood tests and urine tests.

Causes of delirium

Delirium is an acute syndrome that usually as an underlying cause. Conditions that significantly change a person’s brain function can trigger the condition’s onset. These can include:

  • Chronic illness
  • Severe pain
  • Reactions to infections
  • Medications (e.g. benzodiazepines, opioids, antihistamine H1) – medication interactions; side-effects 
  • Medical conditions – heart attack; low blood pressure; low levels of oxygen, high blood sugar, or low blood sugar 
  • Alcohol or drugs – excessive use or sudden withdrawal
  • Social isolation

Prevention of delirium

Given the right conditions and by identifying and removing the cause, delirium is reversible. Preventing delirium is possible by identifying risk factors in individuals with predisposing factors such as age or comorbidities and being aware of adding precipitating factors like certain psychoactive medications.[3] 

Minimizing the risk factors for delirium is vital in preventing it, not only for the individual but for carers, family members and healthcare professionals.

Critical factors that can increase the risk of delirium are:

  • 65 years of age or older
  • A clinical condition that is deteriorating
  • Medical illness
  • Cognitive impairment (past or present)
  • Use of psychoactive drugs

Treatment of delirium

When treating delirium, medical professionals will always aim to treat the underlying condition that is causing or linked to it first. For example, if someone is experiencing low blood pressure or lack of oxygen to the brain, these symptoms will be addressed before further treatment for delirium is given.[5]

Doctors may also administer antibiotics if the delirium is stemming from an infection, as well as ceasing any nonessential medication that may be exacerbating the condition. 

Once any underlying health conditions have been seen to, nursing staff will work to ensure the patient is comfortable and in a calming setting to ensure the delirium abates smoothly. 

Common techniques used to calm those suffering from delirium are:

  • Mobility – ensuring the patient can move comfortably (sometimes with the aid of wheelchairs or walking frames)
  • Environment – Keeping the patient’s room calm, clean, and quiet
  • Routine – ensuring that sleep patterns, eating, exercise, and hygiene are all upheld daily
  • Drink – plenty of water and other hydrating fluids
  • Medications – Managing the patient intake of new and prescribed antipsychotic medications to ensure they do not impact on delirium symptoms
  • Manage pain – Ensuring that any physical discomfort caused by delirium is kept to a minimum

Pharmacological Treatments

It is rare that delirium will be treated with direct medication in the first instance. However, certain symptoms such as psychosis may pose a threat to the individual or others and further treatment will require pharmacological intervention first. 

Medications used to treat aggressive delirium symptoms include:

Self-care for delirium

Individuals – together with carers and family members – can contribute to the improvement of their condition and its prevention moving forward. Awareness of the risk and susceptibility factors above can provide the basis for proactive self-care management of delirium.

  • Establish and maintain an organized environment; be aware of time, such as clocks and calendars, as these help to orient to reality
  • Set reasonable routines for eating and sleeping well
  • Entertain family and friends regularly
  • Make use of aids such as eyeglasses, hearing aids and dentures
  • Have positive thoughts and dwell on positive things
  • Schedule clinical follow-ups: maintain good physical and mental health; address any medical concerns

Helping someone with delirium

It is a good idea for caregivers (family or friends) to discuss the person’s short- and long-term needs with a health care provider and develop a treatment plan. The goal of supportive care is to assist in maintaining good mental function and physical health, not aggravate delirium, and prevent additional complications.

Ways to accomplish this are very similar to those of self-care for delirium. Here are some things to do:

  • Encourage the individual to maintain reasonable routines; avoid stressful, ambiguous situations 
  • Maintain regular sleep-wake cycles as part of their routine to avoid sleep deprivation
  • Ensure that the person consumes sufficient nourishing foods and liquids
  • Encourage physical movement (assist them if necessary to avoid slips, trips or falls)
  • Encourage visits from family and friends but avoid over-stimulation such as multiple visitors and loud noises. Maintain a calm, uncluttered environment
  • Be patient in explaining things and orienting them in the environment
  • Avoid under stimulation from complete silence or a darkened room
  • Assist individuals with eating or drinking to minimize and prevent the risk of choking
  • Encourage the use of hearing aids and eyeglasses to maintain reassurance of their environment with familiar objects such as pictures
  • Seek to treat any pain promptly to avoid discomfort

FAQs about delirium

What is the outlook for people with delirium?

Although delirium is a complex psychiatric disorder, the prognosis for complete recovery is generally favourable. However, this is contingent upon immediate diagnosis, appropriate interventions, age, and the individual’s past and current health conditions. 

However, there are some factors that can impair a person’s recovery from delirium even with intervention. Some people experience distressing memories of delirium that can cause anxiety and stress, while others with mental disorders such as dementia can find symptoms of their condition worsen after an incidence of delirium. 

How common is delirium?

Delirium is a common symptom of a wide range of conditions in elderly patients aged 65 years and older. A 2018 study found that 14.7% of patients in UK hospitals over 65 years old had diagnosable delirium, with most being in the higher level of frailty on the Clinical Frailty Scale (CFS).[6]

Delirium vs. Dementia – What is the difference?

Delirium and dementia are two different conditions. The development of delirium is quick, from hours to days, and is reversible once the cause is determined and treated. Dementia develops more slowly, over months or even years, and is not reversible. Delirium is common in patients with dementia, but they are not the same condition. 

  1. American Psychiatric Association. (2013). Neurocognitive disorders. In Diagnostic and statistical manual of mental disorders (5th ed.).
  2. What is Delirium? (n.d.) American Delirium Society. Retrieved Sept 26th, 2022, from
  3. Delirium. (n.d.) MedlinePlus. Retrieved Sept 26th, 2022, from
  4. Delirium tremens: MedlinePlus Medical Encyclopedia. (2016).
  5. Delirium – symptoms, diagnosis and treatment. (n.d.) Alzheimer’s Society. Retreived Sept 26th, 2022, from
  6. Geriatric Medicine Research Collaborative. Delirium is prevalent in older hospital inpatients and associated with adverse outcomes: results of a prospective multi-centre study on World Delirium Awareness Day. BMC Med 17, 229 (2019).
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Cristina Po Wenger
Author Cristina Po Wenger Writer

Cristina Po Wenger is a medical writer and mental health advocate with a Sociology Degree from the University of Stirling.

Published: Nov 23rd 2022, Last edited: Sep 22nd 2023

Brittany Ferri
Medical Reviewer Dr. Brittany Ferri, PhD OTR/L

Dr. Brittany Ferri, PhD, is a medical reviewer and subject matter expert in behavioral health, pediatrics, and telehealth.

Content reviewed by a medical professional. Last reviewed: Nov 25th 2022