Syncope is a symptom, defined by the European Cardiology Society as a transient, self-limited loss of consciousness (TLOC), usually leading to falling. The onset of syncope is relatively rapid, and the subsequent recovery is spontaneous, complete and usually prompt.1 However, for reasons that become clearer later, we prefer the physiologist's definition: “Syncope is a transient loss of consciousness resulting from an insufficient supply of oxygen to the brain”.2

In a population-based study, the incidence of syncope coming to medical attention in childhood and adolescence was 126/100 000.3 Up to 15% of children will experience at least one episode before the age of 18.4

The reported incidence reaches a peak in 15- to 19-year olds and is more common in females. In the population-based study, neurally mediated syncope (NMS) was by far the most frequent type of syncope (75%), cardiac disease was diagnosed in 10%, psychogenic or unexplained TLOC and syncope of unknown cause accounted for 8%, and possible epilepsy accounted for 5%.3 In our recent series, psychogenic or unexplained TLOC was more common (17%) in hospital patients undergoing more specialist investigation and was recognised in young people with concurrent NMS.

The collapse and loss of consciousness that occur during fainting or syncope are due to the abrupt cutting off of the energy substrates to the cerebral cortex. This is usually through a sudden decrease in cerebral perfusion by oxygenated blood from a reduction in cerebral blood flow itself, a drop in the oxygen content or a combination of these.5

There are many variations in clinical phenomenology: syncope can be of gradual or sudden onset, with or without a recalled warning, with hypotonia or an extensor spasm with upper limb abduction and or extension, or hypermotor with chaotic thrashing about. It may be accompanied by …