A change in how a person acts is called altered behavior. A change may include:

• Confusion.
• Disorientation to time and place.
• Unusually aggressive or combative behavior.
• Lethargy, unexplained sleepiness, or the inability to arouse a person from sleep.

Altered behavior can be caused by conditions or substances that may affect the brain, such as:

• Prescription and nonprescription medicine.
• Drug and alcohol abuse or withdrawal.
• Electrolyte imbalances.
• Exposure to toxins, such as carbon monoxide, arsenic, or lead.
• Lack of oxygen to the brain.
• Head injury.
• Seizure.
• Abnormally high blood sugar (ketoacidosis) or abnormally low blood sugar (hypoglycemia).
• Infection, especially in older adults.
• Mental health problems, such as anxiety disorders, depression, or psychosis.
• Blockages in the blood vessels in the brain, such as in a stroke.
• Bleeding in the brain from a head injury or stroke.
• Destruction of brain tissue by a tumor.
• Pressure on brain tissue by a tumor or swelling.

Changes in behavior may be sudden, such as those caused by a stroke or head injury, or gradual, such as those caused by a tumor or swelling in the brain.