Signs and symptoms of delirium usually begin over a few hours or a few days. They often fluctuate throughout the day, and there may be periods of no symptoms. Symptoms tend to be worse during the night when it's dark and things look less familiar. Primary signs and symptoms include those below.

Reduced awareness of the environment

This may result in:

• An inability to stay focused on a topic or to switch topics
• Getting stuck on an idea rather than responding to questions or conversation
• Being easily distracted by unimportant things
• Being withdrawn, with little or no activity or little response to the environment

Poor thinking skills (cognitive impairment)

This may appear as:

• Poor memory, particularly of recent events
• Disorientation — for example, not knowing where you are or who you are
• Difficulty speaking or recalling words
• Rambling or nonsense speech
• Trouble understanding speech
• Difficulty reading or writing

Behavior changes

These may include:

• Seeing things that don't exist (hallucinations)
• Restlessness, agitation or combative behavior
• Calling out, moaning or making other sounds
• Being quiet and withdrawn — especially in older adults
• Slowed movement or lethargy
• Disturbed sleep habits
• Reversal of night-day sleep-wake cycle

Emotional disturbances

These may appear as:

• Anxiety, fear or paranoia
• Depression
• Irritability or anger
• A sense of feeling elated (euphoria)
• Apathy
• Rapid and unpredictable mood shifts
• Personality changes

Types of delirium

Experts have identified three types of delirium:

• Hyperactive delirium. Probably the most easily recognized type, this may include restlessness (for example, pacing), agitation, rapid mood changes or hallucinations, and refusal to cooperate with care.
• Hypoactive delirium. This may include inactivity or reduced motor activity, sluggishness, abnormal drowsiness, or seeming to be in a daze.
• Mixed delirium. This includes both hyperactive and hypoactive signs and symptoms. The person may quickly switch back and forth from hyperactive to hypoactive states.

Delirium and dementia

Dementia and delirium may be particularly difficult to distinguish, and a person may have both. In fact, delirium frequently occurs in people with dementia. But having episodes of delirium does not always mean a person has dementia. So a dementia assessment should not be done during a delirium episode because the results could be misleading.

Dementia is the progressive decline of memory and other thinking skills due to the gradual dysfunction and loss of brain cells. The most common cause of dementia is Alzheimer's disease.

Some differences between the symptoms of delirium and dementia include:

• Onset. The onset of delirium occurs within a short time, while dementia usually begins with relatively minor symptoms that gradually worsen over time.
• Attention. The ability to stay focused or maintain attention is significantly impaired with delirium. A person in the early stages of dementia remains generally alert.
• Fluctuation. The appearance of delirium symptoms can fluctuate significantly and frequently throughout the day. While people with dementia have better and worse times of day, their memory and thinking skills stay at a fairly constant level during the course of a day.

Delirium occurs when the normal sending and receiving of signals in the brain become impaired. This impairment is most likely caused by a combination of factors that make the brain vulnerable and trigger a malfunction in brain activity.

Delirium may have a single cause or more than one cause, such as a combination of a medical condition and drug toxicity. Sometimes no cause can be identified. Possible causes include:

• Certain medications or drug toxicity
• Alcohol or drug intoxication or withdrawal
• A medical condition, such as a stroke, heart attack, worsening lung or liver disease, or an injury from a fall
• Metabolic imbalances, such as low sodium or low calcium
• Severe, chronic or terminal illness
• Fever and acute infection, particularly in children
• Urinary tract infection, pneumonia or the flu, especially in older adults
• Exposure to a toxin, such as carbon monoxide, cyanide or other poisons
• Malnutrition or dehydration
• Sleep deprivation or severe emotional distress
• Pain
• Surgery or other medical procedures that include anesthesia

Several medications or combinations of drugs can trigger delirium, including some types of:

• Pain drugs
• Sleep medications
• Medications for mood disorders, such as anxiety and depression
• Allergy medications (antihistamines)
• Asthma medications
• Steroid medicines called corticosteroids
• Parkinson's disease drugs
• Drugs for treating spasms or convulsions

Any condition that results in a hospital stay, especially in intensive care or after surgery, increases the risk of delirium, as does being a resident in a nursing home. Delirium is more common in older adults.

Examples of other conditions that increase the risk of delirium include:

• Brain disorders such as dementia, stroke or Parkinson's disease
• Previous delirium episodes
• Visual or hearing impairment
• The presence of multiple medical problems

Delirium may last only a few hours or as long as several weeks or months. If issues contributing to delirium are addressed, the recovery time is often shorter.

The degree of recovery depends to some extent on the health and mental status before the onset of delirium. People with dementia, for example, may experience a significant overall decline in memory and thinking skills. People in better health are more likely to fully recover.

People with other serious, chronic or terminal illnesses may not regain the levels of thinking skills or functioning that they had before the onset of delirium. Delirium in seriously ill people is also more likely to lead to:

• General decline in health
• Poor recovery from surgery
• Need for institutional care
• Increased risk of death