It is not unusual to occasionally forget where you put your keys or glasses, where you parked your car, or the name of an acquaintance. As you age, it may take you longer to remember things. Not all older adults have memory changes, but it can be a normal part of aging. This type of memory problem is more often annoying than serious.

Memory loss that begins suddenly or that significantly interferes with your ability to function in daily life may mean a more serious problem is present.

• Dementia is a slow decline in memory, problem-solving ability, learning ability, and judgment that may occur over several weeks to several months. Many health conditions can cause dementia or symptoms similar to dementia. In some cases dementia may be reversible. Alzheimer's disease is the most common cause of dementia in people older than age 65.
• Delirium is a sudden change in how well a person's brain is working (mental status). Delirium can cause confusion, change the sleep-wake cycles, and cause unusual behavior. Delirium can have many causes, such as withdrawal from alcohol or drugs or medicines, or the development or worsening of an infection or other health problem.
• Amnesia is memory loss that may be caused by a head injury, a stroke, substance abuse, or a severe emotional event, such as from combat or a motor vehicle accident. Depending upon the cause, amnesia may be either temporary or permanent.

Confusion or decreased alertness may be the first symptom of a serious illness, particularly in older adults. Health problems that cause confusion or decreased alertness can include:

• Alzheimer's disease.
• Asthma or COPD, which cause a decrease in the amount of oxygen or an increase in the amount of carbon dioxide in the blood.
• Cardiac problems, such as heart failure, coronary artery disease, or irregular heartbeats (arrhythmias), that reduce blood flow.
• Problems from diabetes.
• Kidney or liver failure, which causes high levels of toxins to build up in the blood.
• Malnutrition and vitamin deficiencies caused by problems, such as long-term alcoholism (Wernicke-Korsakoff syndrome).
• Mental health problems, such as depression or schizophrenia.
• Thyroid problems, such as hypothyroidism, myxedema coma, or hyperthyroidism.

Alcohol and many prescription and nonprescription medicines can cause confusion or decreased alertness. These problems may develop from:

• Taking too much of a medicine (overmedicating). Overuse of medicines may be the single biggest cause of memory loss or confusion in older adults.
• Alcohol and medicine interactions. This is a problem, especially for older adults, who may take many medicines at the same time.
• Misusing or abusing a medicine or alcohol.
• Drug intoxication or the effects of withdrawal.

Other causes of confusion or decreased alertness can include:

• A head injury.
• Decreased or blocked blood flow to the brain. This may occur during a transient ischemic attack (TIA) or a stroke.
• Infection, such as a brain abscess, encephalitis, meningitis, or sepsis.
• Reye's syndrome (in people age 20 or younger).
• Sexually transmitted infections, such as syphilis (late-stage) and human immunodeficiency virus (HIV).
• A seizure disorder (epilepsy).
• Brain tumors.