Signs and symptoms
Episodes of vasovagal syncope are typically recurrent and usually occur when the predisposed person is exposed to a specific trigger. Before losing consciousness, the individual frequently experiences early signs or symptoms such as lightheadedness, nausea, the feeling of being extremely hot or cold (accompanied by sweating), ringing in the ears, an uncomfortable feeling in the heart, fuzzy thoughts, confusion, a slight inability to speak or form words (sometimes combined with mild stuttering), weakness and visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, black cloud-like spots in vision, and a feeling of nervousness can occur as well. The symptoms may become more intense over several seconds to several minutes before the loss of consciousness (if it is lost). Onset usually occurs when a person is sitting up or standing.When people lose consciousness, they fall down (unless prevented from doing so) and, when in this position, effective blood flow to the brain is immediately restored, allowing the person to regain consciousness.
If the person does not fall into a fully flat, supine position, and the head remains elevated above the trunk, a state similar to a seizure may result from the bloods inability to return quickly to the brain, and the neurons in the body will fire off and generally cause muscles to twitch very slightly but mostly remain very tense.The autonomic nervous systems physiological state (see below) leading to loss of consciousness may persist for several minutes, so

If patients try to sit or stand when they wake up, they may pass out again
The person may be nauseated, pale, and sweaty for several minutes or hours

Causes
Reflex syncope occurs in response to a trigger due to dysfunction of the heart rate and blood pressure regulating mechanism. When heart rate slows or blood pressure drops, the resulting lack of blood to the brain causes fainting. Vasovagal
Typical triggers include:

Prolonged standing
Emotional stress
Pain
The sight of blood
Fear of needles
Time varying magnetic field (i.e. transcranial magnetic stimulation)

Situational
After or during urination (micturition syncope)
Straining, such as to have a bowel movement
Coughing
Swallowing
Lifting a heavy weight

Carotid sinus
Pressing upon a certain spot in the neck. This may happen when wearing a tight collar, shaving, or turning the head. Pathophysiology
Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes.