Syncope is a syndrome in which loss of consciousness is of relatively sudden onset, temporary (usually less than 1 to 2 minutes), self-terminating, and of usually rapid recovery. Syncope leads to a generalized weakness of muscles with loss of postural tone, inability to stand upright, and loss of consciousness. Once the patient is in a horizontal position, blood flow to the brain is no longer hindered by gravitation and consciousness is regained. Unconsciousness usually lasts for seconds to minutes. Headache and drowsiness (which usually follow seizures) do not follow a syncopal attack. Syncope results from a sudden impairment of brain metabolism usually due to a reduction in cerebral blood flow.

A slower than normal heart rate (in adults, slower than 60 beats per minute).

An anomaly of the complex formed by the Q, R, and S waves, which occur in rapid succession on the electrocardiogram.

Increased variation of beat-to-beat intervals of the heart that occurs in conjunction with the respiratory cycle.

A decreased magnitude of the sensory perception of sound.