The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017


Fainting (medically known as syncope) is a short loss of consciousness with spontaneous recovery, typically due to inadequate delivery of oxygen or blood to the brain. The collection of symptoms that occurs at the onset of fainting is referred to as “presyncope” and includes lightheadedness, fatigue, muscle weakness, and blurred vision. There are three major classes of syncope: neurally mediated (reflex) syncope, cardiac syncope, and syncope due to orthostatic hypotension (European Society of Cardiology, 2009).

Reflex Syncope

Neurally mediated syncope is fainting as a response to a neural stimulus. Extreme emotion such as stress or fear may cause an individual to faint, as well as exercise, hyperventilation (fast breathing), low blood sugar, and even coughing or sneezing. Reflex syncope takes place when the nervous system cannot initiate an appropriate response to a stimulus and causes a change in heart rate or blood pressure. An individual is in danger of fainting if blood pressure or heart rate is too low to meet the oxygen demands of the brain. An example of this is hyperventilation. When an individual breathes too quickly, there is a dramatic tightening of blood vessels resulting in constricted flow to the brain and fainting occurs. Reflex syncope is the most common form of fainting and may affect healthy individuals. Neurally mediated fainting may happen a single time or be reoccurring.

Cardiac Syncope

Cardiac syncope can result from problems arising in the function or structure of the heart, blood vessels, or lungs. Arrhythmia (irregular heartbeat) is the most common cause of cardiac-related fainting. Certain conditions or medications can cause the heart to beat too quickly (tachycardia), too slowly (bradycardia), or too irregularly to meet the needs of the brain. Cardiac syncope can also be the result of structural defects in the cardiac system, though it is a much rarer cause of fainting.

Syncope Due to Orthostatic Hypotension

Orthostatic hypotension syncope, or postural hypotension, is a condition resulting from a sudden change in posture. When an individual stands up quickly, blood pooling in the lower body (due to gravity) must be pumped to the brain to maintain consciousness. If vessels fail to move blood from the body to the brain fast enough, blood pressure in the brain drops and the individual may faint. Orthostatic hypotension commonly occurs in individuals with low blood pressure and the elderly, but it has been known to occur in individuals with diabetes or as a side effect of certain pharmaceuticals. The onset of fainting may be slower in some individuals, and presyncope symptoms may allow the individual to intervene before fainting occurs.


Lack of consciousness is always a cause for concern and, while fainting itself is not particularly dangerous, it may be a symptom of a more serious underlying condition. A doctor will consider a patient’s medical history as well as perform a medical examination in order to properly diagnose the cause of fainting. Individuals who faint frequently may experience a reduction in mobility and self-care and an increase in depression and pain (due to injuries). Fainting is particularly hazardous for elderly individuals, as falls are the fifth leading cause of death for older adults (Rubenstein & Josephson, 2002).

Preventive measures for fainting will vary between individuals, but there are a few tactics that health professionals agree on: first, dehydration makes one more liable to faint, so proper hydration is vital. Second, eating regular meals will prevent fainting caused by low blood sugar. Third and most importantly, syncope sufferers need to recognize their own warning signs, as different individuals will experience unique presyncope symptoms (Syncope Trust and Reflex Anoxic Seizures, 2009). This self-awareness can provide an individual with enough warning to prevent an episode or seek help before losing consciousness.

Kendra DeHay

See also: Aura; Baroreceptors; Diplopia; Dizziness; Reflex; Seizures

Further Reading

European Society of Cardiology. (2009). Guidelines for the diagnosis and management of syncope. European Heart Journal, 30, 2631—2671. http://dx.doi.org/10.1093/eurheartj/ehp298

Rubenstein, Laurence Z., & Karen R. Josephson. (2002). The epidemiology of falls and syncope. Clinics in Geriatric Medicine, 18, 141—158. http://dx.doi.org/10.1016/S0749-0690(02)00002-2

Soteraides, Elpidoforos S., Jane C. Evans, Martin G. Larson, Ming Hui Chen, Leway Chen, Emelia J. Benjamin, & Daniel Levy. (2002). Incidence and prognosis of syncope. New England Journal of Medicine, 347(12), 878—885.

Syncope Trust and Reflex Anoxic Seizures (STARS). (2009). Reflex syncope (Vasovagal syncope). Retrieved from http://www.nhs.uk/ipgmedia/national/syncope%20trust%20and%20reflex%20anoxic%20seizures/assets/reflexsyncope(vasovagalsyncope).pdf