Adults of all ages occasionally forget where they put their keys or glasses, where they parked their car or the name of an acquaintance. Older adults may take longer to retrieve memories. Although not universal, memory changes are a normal part of aging and often more annoying than serious.

Memory loss that begins suddenly or that significantly interferes with daily life is more than ordinary forgetfulness. Examples include:

• Dementia. A condition of slow (over weeks or months) decline in memory, problem-solving ability, learning ability and judgment. Alzheimer's disease is the most common cause of dementia in older adults.
• Delirium. A condition of sudden change in a person's mental status, which leads to confusion, disruption of the sleep-wake cycles and unusual behavior.

A decrease in alertness may lead to a loss of consciousness. Fainting is a form of brief unconsciousness, while coma is a deep, prolonged state of unconsciousness. Both prescription and nonprescription drugs can cause confusion or decreased alertness. Other causes include head injury, exposure to heat or cold, seizure (convulsion), alcohol or drug use, medications and fever.