What is decreased alertness?

Confusion, memory loss, and altered alertness: Overview

It's not unusual to sometimes forget where you put your keys or glasses. Or maybe you forget 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 these changes can be a normal part of aging. This type of memory problem is more often annoying than serious.

Memory loss that starts suddenly or that clearly interferes with how well you can function in daily life may be a sign of a more serious problem.

  • Dementia is a slow decline in memory, problem-solving ability, learning ability, and judgment. It may occur over several weeks to several months. Many health conditions can cause dementia or symptoms like it. Alzheimer's disease is the most common cause of dementia in people older than 65.
  • Delirium is a sudden change in how well a person's brain is working (mental status). It can cause confusion, changes in the sleep-wake cycles, and unusual behavior. It can have many causes. One cause is withdrawal from alcohol or drugs or medicines. It can also be caused by an infection or other health problem that starts or gets worse.
  • Amnesia is memory loss that may be caused by a head injury, a stroke, or substance abuse. It can also be caused by a severe emotional event, such as from combat or a car crash. Amnesia may be either short-term or permanent. It depends on what caused it.

Confusion or decreased alertness may be the first symptom of a serious illness. This happens most in older adults. Health problems that can cause it include:

  • Infections. Examples are urinary tract infections, respiratory infections, and sepsis.
  • Alzheimer's disease.
  • Asthma or COPD. They cause a decrease in the amount of oxygen or an increase in the amount of carbon dioxide in the blood.
  • Cardiac problems that reduce blood flow. Examples are heart failure, coronary artery disease, and irregular heartbeats (arrhythmias).
  • Problems from diabetes.
  • Kidney or liver failure. They cause high levels of toxins to build up in the blood.
  • Malnutrition and vitamin deficiencies caused by health problems. One example is alcohol use disorder (Wernicke-Korsakoff syndrome).
  • Mental health problems, such as depression or schizophrenia.
  • Thyroid problems. These include hypothyroidism, myxedema coma, and 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) or taking medicines that may interact with each other. 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 that often affects older adults, who may take many medicines at the same time.
  • Misusing a medicine or alcohol use disorder.
  • 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.
  • Sexually transmitted infections, such as syphilis (late-stage) and human immunodeficiency virus (HIV).
  • A seizure disorder (epilepsy).
  • Brain tumors.

Conditions in the environment that can cause changes in the level of consciousness include:

  • Cold temperature exposure. It can lead to hypothermia.
  • High temperature exposure. It can lead to heatstroke.
  • Hospitalization. This often affects older adults when their environment and routines are changed.
  • Decreased oxygen in the blood (hypoxia) from high altitude.
  • Exposure to toxins (poisons), such as carbon monoxide.

Many times there are other symptoms, such as a fever, chest pain, or not being able to walk or stand. It's important to look for and tell your doctor about other symptoms you have when confusion or decreased alertness occurs. This can help your doctor find the cause of your symptoms.

A decrease in alertness may progress to loss of consciousness. A person who loses consciousness isn't awake or aware of his or her surroundings. Fainting (syncope) is a form of brief unconsciousness. Coma is a deep, prolonged state of unconsciousness.

What are the symptoms of confusion or decreased alertness?

Many health problems cause confusion or decreased alertness. It is not unusual for a person who is sick to be sleepy or confused when he or she wakes up. But extreme sleepiness may be a symptom of a more serious health problem.


Confusion may range from mild to severe. Symptoms of confusion may include:

  • Jumbled or disorganized thoughts.
  • Unusual, bizarre, or aggressive behavior.
  • Having trouble solving problems or doing tasks that used to be easy for you.
  • Not knowing where you are or not recognizing family members or familiar items.
  • Firmly held but false beliefs (delusions).
  • Seeing, hearing, feeling, smelling, or tasting things that are not really there (hallucinations or illusions).
  • Unfounded suspicions that others are after you or want to harm you (paranoia).

Decreased alertness

Decreased alertness occurs when a person is not fully awake, aware of, or able to respond normally to his or her external environment. Decreased alertness may also mean that a chronic illness has gotten worse.

What causes confusion or decreased alertness?

A sudden change in the mental state or level of consciousness may be caused by:

  • A head injury. Serious head injuries may cause injuries to the brain.
  • Decreased or blocked blood flow to the brain. This may occur during a transient ischemic attack (TIA) or a stroke.
  • A seizure disorder (epilepsy).
  • A disease, such as a brain tumor or problems from diabetes.
  • Environmental factors, such as dehydration, cold temperature exposure (hypothermia), and heatstroke.
  • Medicines and alcohol or drug use or problems caused by quitting their use (withdrawal).
  • Infection, especially an infection of the nervous system.
  • Shock that is caused by infection that has spread throughout the blood and tissues (sepsis).
  • Heart problems, such as a heart attack, an irregular heart rhythm (arrhythmia), or heart failure.
  • Thyroid problems, such as hyperthyroidism.
  • Low oxygen levels from chronic obstructive pulmonary disease (COPD), pulmonary embolism (PE), or altitude sickness.
  • Metabolism problems from liver or kidney failure.
  • Mental health problems, such as depression or schizophrenia.

Other problems that may lead to confusion or decreased alertness include:

  • Decreased hearing or vision.
  • Electrolyte imbalances, such as low levels of sodium and potassium in the blood.
  • Low blood sugar (hypoglycemia) or high blood sugar (hyperglycemia).
  • Malnutrition and vitamin deficiencies.
  • Sleep problems, such as the inability to fall asleep or stay asleep (insomnia) or sleep apnea.

A complete medical examination may be needed before the cause of your confusion or decreased alertness can be diagnosed. Treatment depends on the cause of the problem. Contact your doctor for an exam if you are having problems with confusion or decreased alertness.

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The content above contains general health information provided by Healthwise, Incorporated, and reviewed by its medical experts. This content should not replace the advice of your healthcare provider. Not all treatments or services described are offered as services by us. For recommended treatments, please consult your healthcare provider.