Unconsciousness can be caused by nearly any major illness or injury. It can also be caused by substance (drug) and alcohol use. Choking on an object can result in unconsciousness as well.

Brief unconsciousness (or fainting) is often a result from dehydration, low blood sugar, or temporary low blood pressure. It can also be caused by serious heart or nervous system problems. A doctor will determine if the affected person needs tests to diagnose their fainting.

Other causes of fainting include straining during a bowel movement or urination, coughing very hard, breathing very fast (hyperventilating), or vasovagal syncope.

The person will be unresponsive (does not respond to activity, touch, sound, or other stimulation).

The following symptoms may occur after a person has been unconscious:

• Amnesia for (not remembering) events before, during, and even after the period of unconsciousness
• Confusion
• Drowsiness
• Headache
• Inability to speak or move parts of the body (stroke symptoms)
• Lightheadedness
• Loss of bowel or bladder control (incontinence)
• Rapid heartbeat (palpitations)
• Slow heartbeat
  
• Stupor (severe confusion and weakness)

If the person is unconscious from choking, symptoms may include:

• Inability to speak
• Difficulty breathing
• Noisy breathing or high-pitched sounds while inhaling
• Weak, ineffective coughing
• Bluish skin color

Being asleep is not the same as being unconscious. A sleeping person will respond to loud noises or gentle shaking. An unconscious person will not.

If someone is awake but less alert than usual, ask a few simple questions, such as:

• What is your name?
• What is the date?
• How old are you?

Wrong answers or not being able to answer the question suggest a change in mental status.

If a person is unconscious or has a change in mental status, follow these first aid steps:

Call or tell someone to call 911 or the local emergency number.

1. Check the person's airway, breathing, and pulse frequently. If necessary, begin CPR.
2. If the person is breathing and lying on their back, and you do not think there is a spinal injury, carefully roll the person toward you onto their side. Bend the top leg so both hip and knee are at right angles. Gently tilt their head back to keep the airway open. If breathing or pulse stops at any time, roll the person onto their back and begin CPR.
3. If you think there is a spinal injury, leave the person where you found them (as long as breathing continues). If the person vomits, roll the entire body at one time to their side. Support their neck and back to keep the head and body in the same position while you roll.
4. Keep the person warm until medical help arrives.
5. If you see a person fainting, try to prevent a fall. Lay the person flat on the floor and raise their feet about 12 inches (30 centimeters).
6. If fainting is likely due to low blood sugar, give the person something sweet to eat or drink only when they become conscious.

If the person is unconscious from choking:

• Begin CPR. Chest compressions may help dislodge the object.
• If you see something blocking the airway and it is loose, try to remove it. If the object is lodged in the person's throat, DO NOT try to grasp it. This can push the object farther into the airway.
• Continue CPR and keep checking to see if the object is dislodged until medical help arrives.

• DO NOT give an unconscious person any food or drink.
• DO NOT leave the person alone.
• DO NOT place a pillow under the head of an unconscious person.
• DO NOT slap an unconscious person's face or splash water on their face to try to revive them.

Call 911 or the local emergency number if the person is unconscious and:

• Does not return to consciousness quickly (within a minute)
• Has fallen down or been injured, especially if they are bleeding
• Has diabetes
• Has seizures
• Has lost bowel or bladder control
• Is not breathing
• Is pregnant
• Is over age 50

Call 911 or the local emergency number if the person regains consciousness, but:

• Feels chest pain, pressure, or discomfort, or has a pounding or irregular heartbeat
• Cannot speak, has vision problems, or cannot move their arms and legs

To prevent becoming unconscious or fainting:

• Avoid situations where your blood sugar level gets too low.
• Avoid standing in one place too long without moving, especially if you are prone to fainting.
• Get enough fluid, particularly in warm weather.
• If you feel like you are about to faint, lie down or sit with your head bent forward between your knees.

If you have a medical condition, such as diabetes, always wear a medical alert necklace or bracelet.

Loss of consciousness - first aid; Coma - first aid; Mental status change; Altered mental status; Syncope - first aid; Faint - first aid 

American Red Cross. First Aid/CPR/AED Participant's Manual. 2nd ed. Dallas, TX: American Red Cross; 2016. www.pdfdrive.com/american-red-cross-first-aidcpraed-d128296673.html. Accessed February 20, 2023.

Kleinman ME, Goldberger ZD, Rea T, et al. 2017 American Heart Association focused update on adult basic life support and cardiopulmonary resuscitation quality: an update to the American Heart Association Guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2018;137(1):e7-e13. PMID: 29114008 pubmed.ncbi.nlm.nih.gov/29114008/.

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.

Papa L, Meurer WJ. Stroke. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 87.

Probst M. Syncope. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 11.

Updated by: Jesse Borke, MD, CPE, FAAEM, FACEP, Attending Physician at Kaiser Permanente, Orange County, CA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.