Many conditions can cause decreased alertness, including:

• Chronic kidney disease
• Extreme tiredness or lack of sleep
• High blood sugar or low blood sugar
• High or low blood sodium concentration
• Infection that is severe or involves the brain
• Liver failure
• Thyroid conditions that cause low thyroid hormone levels or very high thyroid hormone levels

Brain disorders or injury, such as:

• Dementia or Alzheimer disease (advanced cases)
• Head trauma (moderate to severe cases)
• Seizure
• Stroke (usually when the stroke is either massive or has destroyed certain areas of the brain such as the brainstem or thalamus)
• Infections that affect the brain, such as meningitis or encephalitis

Injury or accidents, such as:

• Diving accidents and near drowning
• Heat stroke
• Very low body temperature (hypothermia)

Heart or breathing problems, such as:

• Abnormal heart rhythm
• Lack of oxygen from any cause
• Low blood pressure
• Severe heart failure
• Severe lung diseases
• Very high blood pressure

Toxins and drugs, such as:

• Alcohol use (binge drinking or damage from long-term alcohol use)
• Exposure to heavy metals, hydrocarbons, or toxic gases
• Overuse of drugs such as opiates, narcotics, sedatives, and anti-anxiety or seizure medicines
• Side effect of almost any medicine, such as those used to treat seizures, depression, psychosis, and other illnesses

Get medical help for any decrease in consciousness, even when it is due to alcohol intoxication, fainting, or a seizure disorder that has already been diagnosed.

People with epilepsy or other seizure disorders should wear a medical ID bracelet or necklace describing their condition. They should avoid situations that have triggered a seizure in the past.

Get medical help if someone has decreased alertness that cannot be explained. Call 911 or the local emergency number if normal alertness does not return quickly.

Most often, a person with decreased consciousness will be evaluated in an emergency room.

The health care provider will perform a physical exam. The exam will include a detailed look at the heart, breathing, and nervous system.

The health care team will ask questions about the person's medical history and symptoms, including:

Time pattern

• When did the decreased alertness happen?
• How long did it last?
• Has it ever happened before? If so, how many times?
• Did the person behave the same way during past episodes?

Medical history

• Does the person have epilepsy or a seizure disorder?
• Does the person have diabetes?
• Has the person been sleeping well?
• Has there been a recent head injury?

Other

• What medicines does the person take?
• Does the person use alcohol or illicit drugs on a regular basis?
• What other symptoms are present?

Tests that may be done include:

• Chest x-ray
• Complete blood count (CBC) or blood differential
• CT scan or MRI of the head
• Oxygen level (pulse oximetry or blood gas)
• Electrocardiogram (ECG)
• Electroencephalogram (EEG)
• Metabolic panel and liver function tests
• Toxicology panel and blood alcohol level
• Urinalysis

Treatment depends on the cause of the decreased alertness. How well a person does depends on the cause of the condition.

The longer the person has had decreased alertness, the worse the outcome.

Stuporous; Mental status - decreased; Loss of alertness; Decreased consciousness; Changes in consciousness; Obtundation; Coma; Unresponsiveness

Berger JR, Price R. Stupor and coma. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 5.

Greer DM, Bernat JL. Coma, disorders of consciousness, and brain death. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 373.

Lei C, Smith C. Depressed consciousness and coma. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 12.

Updated by: Joseph V. Campellone, MD, Department of Neurology, Cooper Medical School at Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.