Syncope, also known as fainting, is defined as a short loss of consciousness and muscle strength, characterized by a fast onset, short duration, and spontaneous recovery. It is due to a decrease in blood flow to the entire brain usually from low blood pressure. Some causes have prodromal symptoms before the loss of consciousness occurs. These symptoms may include lightheadedness, sweating, pale skin, blurred vision, nausea, vomiting, and feeling warm, among others. Syncope may also be associated with a short episode of muscle twitching. If a person does not completely lose consciousness and muscle strength it is referred to as presyncope. It is recommended that presyncope be treated the same as syncope.
Causes range from non-serious to potentially fatal. There are three broad categories of causes: heart or blood vessel related,reflex also known as neurally mediated, and orthostatic hypotension. Issues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common. Heart related causes may include anabnormal heart rhythm, problems with the heart valves or heart muscle and blockages of blood vessels from a pulmonary embolism or aortic dissection among others. Neurally mediated syncope occurs when blood vessels expand and heart rate decreases inappropriately. This may occur from either a triggering event such as exposure to blood, pain or strong feelings or a specific activity such as urination, vomiting, or coughing. This type of syncope may also occur when an area in the neck known as the carotid sinus is pressed. The final type of syncope is due to a drop in blood pressure from standing up. This is often due to medications that a person is taking but may also be related to dehydration, significant bleeding or infection
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