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.
Other causes of fainting include straining during a bowel movement (vasovagal syncope), coughing very hard, or breathing very fast (hyperventilating).
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 events before, during, and even after the period of unconsciousness
If the person is unconscious from choking, symptoms may include:
Inability to speak
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.
Check the person's airway, breathing, and pulse frequently. If necessary, begin CPR.
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.
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.
Keep the person warm until medical help arrives.
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.
If fainting is likely due to low blood sugar, give the person something sweet to eat or drink 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.
When to Contact a Medical Professional
Call 911 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 lost bowel or bladder control
Is not breathing
Is over age 50
Call 911 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
Berg RA, Hemphill R, Abella BS, et al. Part 5: Adult basic life support: 2010 American Heart Association Guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(18 Supple 3):S685-705. PMID: 20956221 www.ncbi.nlm.nih.gov/pubmed/20956221.
Jacob L. Heller, MD, MHA, Emergency Medicine, Virginia Mason Medical Center, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.