Delirium is a syndrome (group of symptoms) characterized by a sudden onset of altered sensorium (decreased awareness of one's environment). confusion, and disorientation (impaired sense of time, surroundings, or known people).

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

• Infections: Delirium can result from infections of the brain (meningitis and encephalitis etc).
• Metabolic problems and endocrine abnormalities. Deliriuma can be caused by thyroid problems, hypoglycemia, too little or too much sodium or calcium, and an impaired ability to absorb vitamin B-12.
• Immune system disorders. A  side effect of your body's attempt to fight off an infection (auto immune disorder) can result in delirium e.g. multiple sclerosis. Conditions that cause a completely compromised immune system, such as leukemia can also cause delirium.
• Nutritional deficiencies. Symptoms of delirium can  occur as a result of damage to brain cells by dehydration, and deficiencies in vitamins B-1, B-6 and B-12.
• Insufficient oxygen. Delirium can occur when not enough oxygen gets to organ tissue due to heart attack, severe asthma, chronic lung problems or a heart condition that deprives the brain of the oxygen it needs, carbon monoxide poisoning, strangulation, high-altitude exposure.
• Reactions to medications. Delirium may occur as a reaction to a single medication or because of an interaction of several drugs including sleep medications, narcotic pain relievers, antidepressants, Parkinson's disease treatments, drugs for treating convulsions, allergy medications etc.
• Exposure to poisons. Exposure to heavy metals, such as lead or manganese, and other poisons, such as pesticides can cause delirium as can excessive use of alcohol and recreational drugs also sometimes display symptoms.
• Brain tumors. Delirium can be the result of damage caused by a brain tumor or a bleed in the brain.

 Factors that may make people more vulnerable to the development of delirium include:

• Dementia
• Older age
• Visual or hearing impairment
• Poor nutrition or dehydration
• Severe, chronic or terminal illness
• Multiple medical problems
• HIV/AIDS
• Treatment with multiple drugs
• Alcohol or drug abuse

• Medications
• Surgery
• Sudden, severe illness
• Infection
• Alcohol or drug withdrawal
• Emotional stress
• Hospital admission especially in the intensive care unit

Symptoms:

Symptoms of delirium often fluctuate throughout the day. Therefore, a person with delirium may have periods with no symptoms alternating with periods with severe symptoms. The primary symptoms of delirium include:

Reduced awareness of the environment

• An inability to stay focused on a topic
• Wandering attention
• Getting stuck on an idea rather than responding to questions or conversation
• Being easily distracted by unimportant things

Cognitive impairment, or poor thinking skills

• Poor memory, particularly of recent events
• Disorientation, or not knowing where one is, who one is or what time of day it is
• Difficulty speaking or recalling words
• Rambling or nonsense speech
• Difficulty understanding speech
• Difficulty reading or writing

Other common symptoms

• Seeing things that don't exist (hallucinations)
• Agitation, irritability or combative behavior
• Little or no activity or little response to the environment
• Disturbed sleep habits
• Extreme emotions, such as fear, anxiety, anger or depression