What Is Delirium? Symptoms and Treatments Explained

Dementia can greatly affect someone’s behaviour and communication. But someone who is usually mostly independent may, over the course of an afternoon, become deeply confused, unusually sleepy, or unexpectedly distressed and paranoid.

In moments like these, it is natural to worry that their dementia has suddenly become worse. However, a sharp change in someone’s thinking, behaviour or alertness should not automatically be assumed to be part of their dementia.

One possible explanation is delirium. This is a serious medical condition that develops quickly and is usually caused by an underlying physical problem. As some causes of sudden confusion can be serious, it is important to seek medical advice rather than waiting to see if the changes disappear on their own.

What Is Delirium?

Delirium is a sudden change in a person’s mental state that develops over a short period of time, usually within hours or one to two days. It can affect attention, awareness, thinking, perception, and behaviour.

Unlike dementia, which usually develops gradually, delirium is an acute medical problem. It is often the brain’s response to another physical problem, such as an infection, dehydration, pain, medication effects, or a serious illness.

Delirium can improve once the underlying cause is identified and treated, but recovery is not always immediate. Some people continue to experience problems with thinking and memory for weeks or even months afterwards.

It primarily affects:

• Attention and awareness: Difficulty focusing, staying awake, or paying attention.
• Cognition: Confusion, memory issues, or disorganised thinking.
• Perception: Visual or auditory hallucinations, or misinterpreting surroundings.
• Behavior and mood: Sudden agitation, extreme quietness, restlessness, or fearfulness.

These symptoms can occur for a variety of reasons, especially in older people or those with dementia. However, three key features can help distinguish delirium from other changes in mental function:

1. Rapid onset: Symptoms develop quickly, usually over several hours or one to two days.
2. Fluctuation: Symptoms can change considerably over the course of a day. Someone may appear relatively settled at one point and then become much more confused, drowsy, or agitated later.
3. An underlying cause: Delirium is usually linked to another health problem or physical stress, such as an infection, dehydration, pain, medication effects, or a recent operation. There may be more than one contributing cause.

What Are the Symptoms of Delirium?

As delirium affects several aspects of mental functioning, its symptoms can vary considerably from one person to another. The most important clue is often a sudden change from the person’s usual behaviour or abilities.

Sudden Changes in Awareness and Attention

• Struggling to track conversations or getting easily distracted.
• Appearing unusually slow to respond to basic questions.
• Drifting off midway through a task or sentence.

Disorientation and Communication Difficulties

• Sudden uncertainty about where they are or what time of day it is.
• Suddenly struggling to recognise familiar surroundings or people they would normally know.
• Struggling to find common words, speaking incoherently, or rambling.

Changes in Behavior, Mood, and Perception

• Sudden anxiety, fearfulness, irritability, or unusual anger.
• Seeing or hearing things that are not there (hallucinations).
• Becoming unusually suspicious or developing strong beliefs that are not based in reality, such as believing that family members or care staff are trying to harm or deceive them.

Physical and Functional Changes

• Sudden unsteadiness or loss of mobility.
• Loss of appetite or refusing food and fluids.
• Disrupted sleep patterns (staying awake all night and sleeping all day).

The Three Types of Delirium

Delirium does not look the same in everyone. There are three main types that are categorised depending on changes in alertness and activity.

• Hyperactive Delirium: The person may become restless, agitated, unusually alert, or distressed. They may pace, resist care, or experience hallucinations.
• Hypoactive Delirium: The person may become unusually quiet, withdrawn, sluggish, or sleepy. They may interact less with people around them, move less, or eat and drink less. This type can be particularly easy to miss and passed off as tiredness or a worsening of dementia.
• Mixed Delirium: The person experiences a mixture of hyperactive and hypoactive symptoms, sometimes changing from one state to another during the same day.

What Causes Delirium?

Delirium is usually caused by an underlying health problem, and there may be more than one contributing factor. Common causes and triggers include:

• Infections: Urinary tract infections (UTIs), chest infections (pneumonia), skin infections (cellulitis), and systemic viral or bacterial illnesses.
• Dehydration and malnutrition: Not drinking enough or changes in the body’s fluid and electrolyte balance can affect how the brain functions.
• Constipation and urinary retention: Being unable to empty the bowel or bladder can cause significant discomfort and contribute to delirium.
• Pain or physical injury: This can include pain following a fall, fracture, or operation.
• Medication: Some medicines can contribute to delirium, particularly when a new medicine is started, doses change, medicines interact, or certain medicines are stopped suddenly.
• Surgery and anesthesia: Delirium can occur after major operations, particularly in older or medically vulnerable people.
• Changes in surroundings: An unfamiliar or disorienting environment, poor sleep, and missing glasses or hearing aids can increase the risk, particularly in someone who is already vulnerable.

Who Is Most at Risk?

While anyone can develop delirium during severe illness, certain factors make individuals much more vulnerable:

• Existing dementia or cognitive impairment: Dementia is the largest risk factor for developing delirium.
• Age 65 or older: Vulnerability increases significantly with age.
• Severe illness or frailty: Multiple chronic health conditions or recent major surgery.
• History of delirium: Having experienced delirium during past illnesses.
• Sensory impairments: Hearing or visual loss, which makes interpreting unfamiliar surroundings more difficult.

Delirium is particularly common among older people in hospital. The Royal College of Psychiatrists reports that around 20–30% of people on general medical wards experience delirium, while it affects around 10–50% of people following surgery.

Delirium vs Dementia

As delirium and dementia share symptoms like memory loss and confusion, they are easily confused. However, their patterns, causes, and treatments are completely different.

If someone suddenly becomes much more confused, sleepy, agitated or less able to communicate than they normally are, this should not simply be attributed to their dementia. Delirium is one possible explanation and needs prompt medical assessment.

Is Delirium a Medical Emergency?

Sudden confusion should always be taken seriously. Delirium can be caused by an underlying medical problem that needs prompt treatment, and some causes of sudden confusion can be life-threatening.

If someone suddenly becomes confused or their mental state changes dramatically, seek urgent medical help. The NHS advises going to A&E or calling 999 if someone suddenly becomes confused. If the situation is less immediately difficult but you are concerned about a sudden change, NHS 111 or a GP can provide urgent advice.

While waiting for medical help:

• Stay with the person if possible.
• Speak calmly and use short, simple sentences.
• Reassure them and explain who you are and where they are.
• Note when the changes began.
• Have a list of their medicines available if possible.
• Do not try to diagnose or treat the cause yourself.

How Is Delirium Diagnosed?

Diagnosis focuses on identifying a sudden change from the person’s usual level of functioning. A healthcare professional may use a screening tool called the 4AT when delirium is suspected. It looks at four areas:

• Alertness: Whether the person is unusually sleepy or unusually alert.
• AMT4: Simple questions about areas such as age, date of birth, place, and the current year.
• Attention: Whether the person can concentrate on a simple mental task.
• Acute change or fluctuating course: Whether there has been a recent change in mental state or symptoms that come and go.

The 4AT can help identify possible delirium, but it is part of a professional assessment rather than a diagnostic test for families to use themselves. A trained healthcare professional should carry out the assessment with a specialist to confirm the diagnosis where indicated.

How Is Delirium Treated?

There is no single treatment that cures delirium. The main approach is to identify what is causing the delirium and treat that underlying problem. Depending on the cause, treatment may include:

• Treating an infection.
• Correcting dehydration.
• Providing pain relief.
• Treating constipation or urinary retention.
• Reviewing medicines that may be contributing.
• Correcting problems with blood sugar, electrolytes or oxygen levels.
• Treating injuries or other acute illnesses.

There may be more than one cause, so healthcare professionals may need to investigate several possible problems at the same time. Alongside medical treatment, a calm and familiar environment can support recovery. Family members, carers and healthcare professionals can help by supporting eating and drinking, maintaining a healthy sleep routine and helping the person move around safely.

Medication is not routinely used to treat delirium itself. If a person is severely distressed or considered a risk to themselves or others, and de-escalation techniques have not worked or are not appropriate, a doctor may consider a short course of an antipsychotic such as haloperidol.

NICE recommends using the lowest clinically appropriate dose for the shortest possible period, usually no more than one week. These medicines need particular caution in older people and may be unsuitable for people with conditions such as Parkinson’s disease or dementia with Lewy bodies.

The purpose of this medication is to manage severe distress or risk. It does not treat the underlying cause of delirium.

Can Delirium Be Prevented?

Not every case of delirium can be prevented, particularly when someone is seriously ill. However, reducing avoidable risk factors can lower the likelihood of it developing. Preventative measures may include:

• Hydration: Encouraging regular fluids and identifying signs of dehydration.
• Nutrition: Supporting the person to eat enough and addressing problems that affect their appetite.
• Mobility: Encouraging safe movement and avoiding unnecessary bed rest.
• Pain management: Looking for signs of pain, including non-verbal signs in someone who has difficulty communicating.
• Sleep: Supporting a normal day-and-night routine and avoiding unnecessary disturbance overnight.
• Sensory support: Making sure glasses and hearing aids are available, clean, and working properly.
• Familiarity: Using familiar objects, routines and people where possible.
• Medication reviews: Checking whether medicines could be contributing to delirium risk.

How Long Does Delirium Last?

Recovery from delirium varies considerably. For some people, symptoms improve within a few days once the underlying cause has been treated. Others may take considerably longer to recover, particularly after serious illness or major surgery.

The NHS reports that symptoms disappear within six days in around 60% of people, but this should not be treated as a fixed recovery time for everyone. Some people continue to have problems with memory and thinking after delirium has ended. Prolonged or severe delirium is also associated with a greater risk of later cognitive decline.

Some people continue to experience difficulties with memory and thinking for weeks or even months after the acute episode. A person may also need more support with everyday activities while they recover. 

However, this does not mean that delirium simply causes dementia. In someone who already has underlying problems with memory and thinking, delirium may contribute to a faster decline or make previously unnoticed difficulties more apparent.

The Role of Care Homes in Managing Delirium

Care home staff can support early recognition of delirium as they often know a resident’s usual routines, communication style, and level of independence. A sudden change, such as becoming unusually sleepy during the day, refusing meals, becoming much more confused, or behaving differently from usual, can be a sign that something is wrong.

Care teams can support early recognition by monitoring changes in behaviour, eating and drinking, mobility and alertness, while ensuring that concerns are escalated promptly to the appropriate healthcare professional.

Families can also play an important role. If you notice that your relative is behaving very differently from normal, tell the care team. Your knowledge of their usual behaviour can provide valuable information when assessing a possible change in their health.

When to Seek Urgent Medical Help

Seek urgent medical advice if someone suddenly develops:

• Confusion or disorientation.
• Unusual drowsiness or difficulty staying awake.
• Sudden agitation, distress or fear.
• Hallucinations or unusual suspiciousness.
• Difficulty following a conversation or communicating.
• A sudden change in eating, drinking or mobility.

For someone who suddenly becomes confused, the NHS advises urgent assessment because some causes can be serious or life-threatening. If the person lives with dementia, don’t assume that a sudden change is simply the next stage of their condition. Their usual behaviour and abilities provide an important baseline for recognising delirium.

Delirium can be a very frightening experience. The sudden changes in confusion, alertness, behaviour and communication can make it difficult to know whether their dementia has progressed or whether something else is wrong.

The key difference is often the speed of the change. Dementia usually develops gradually, while delirium can appear over hours or a few days and fluctuate considerably.

As delirium is often linked to an underlying health problem, take sudden changes seriously and assess them promptly. Treating the cause is the most effective way to support recovery.

For families and care teams, knowing someone’s usual behaviour is one of the most useful ways to recognise when something has changed.