Understanding Fainting -- the Basics

In this article

• What Is Fainting?
• What Causes Fainting?

What Causes Fainting? continued...

• Diseases of the autonomic nervous system. Your autonomic nervous system is the part of the nervous system that controls involuntary vital functions, such as the beating of your heart, the degree to which your blood vessels are constricted, and breathing. Autonomic nervous system problems include acute or subacute dysautonomia, chronic post-ganglionic autonomic insufficiency, and chronic pre-ganglionic autonomic insufficiency. If you have one of these disorders, you are likely to have other symptoms, such as erectile dysfunction (inability to have or maintain an erection), loss of bladder and bowel control, loss of the normal reflexes of your pupils, or decreased sweating, tearing, and salivation.
• Conditions that interfere with the parts of the nervous system that regulate blood pressure and heart rate. These conditions include diabetes, alcoholism, malnutrition, and amyloidosis (in which waxy protein builds up in the tissues and organs). If you take certain high blood pressure drugs, which act on your blood vessels, you may be more likely to suffer from fainting. If you are dehydrated, which may affect the amount of blood in your body and, thus, your blood pressure, you may be more likely to faint.
• Heart or blood vessel problems that interfere with blood flow to the brain. These may include heart block (a problem with the electrical impulses that control your heart muscle), problems with the sinus node (a specialized area of your heart that helps it beat), heart arrhythmia (irregular heart rhythm), a blood clot in the lungs, an abnormally narrowed aortic heart valve, or certain other problems with the structure of your heart.
• Conditions that may cause unusual patterns of stimulation to particular nerves. These include micturition syncope (fainting during or after urination), glossopharyngeal neuralgia (fainting due to inflammation and pain in a particular nerve to the mouth); cough syncope (fainting after intense coughing), and stretch syncope (fainting that occurs when stretching the neck and arms).
• Hyperventilation. If you become intensely anxious or panicked and breathe too quickly, you may feel faint from hyperventilation (taking in too much oxygen and getting rid of too much carbon dioxide too quickly).