Confusion is the inability to think with your usual speed or clarity, including feeling disoriented and having difficulty paying attention, remembering, and making decisions.

Disorientation; Thinking - unclear; Thoughts - cloudy

Confusion may come on quickly or slowly over time, depending on the cause. Many times, confusion is temporary. Other times it is permanent and not curable.

Confusion is more common in the elderly, and often occurs during a hospital stay.

Some confused people may act aggressively.

• Alcohol intoxication
• Brain tumor
• Concussion
• Fever
• Fluid and electrolyte imbalance
• Head trauma or head injury
• Illness in an elderly person
• Infections
• Lack of sleep (sleep deprivation)
• Low blood sugar
• Low levels of oxygen (for example, from chronic lung disorders)
• Medications
• Nutritional deficiencies, especially niacin, thiamine, vitamin C, or vitamin B12
• Seizures
• Sudden drop in body temperature (hypothermia)

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Bazakis AM, Kunzler C. Altered mental status due to metabolic or endocrine disorders. Emer Med Clinics of North America. 2005;23(3):901-908.

Biem J. Out of the cold: management of hypothermia and frostbite. CMAJ. 2003;168(3):305-311.