A form of stituational syncope that is preceded by or associated with intense laughing
Syncope, which is the medical term for fainting, is generally caused by cerebral ischemia. Ischemia results when there is not enough oxygenated blood reaches the brain due to an abrupt drop of blood pressure. There are many forms of syncope, such as micturition syncope, tussive syncope, and swallowing syncope.
Laughter-induced syncope is a rare form of syncope. It is a situational syncope in such a way that fainting occurs following an intense laughter. Cox et al. reported a case of laughter-induced syncope which they called Seinfeld syncope since syncope occurred while watching the television show Seinfeld.1
Another reported case is an elderly man with a twenty-year history of syncope and on one occasion he fainted after an intense laughter. The patient reported to experience prodromal symptoms while laughing prior to syncope. Braga et al. presumed that the possible cause of this form of syncope is connected to Valsalva maneuver. Accordingly, following the phase I of the maneuver (which is a shoot in blood pressure and the eventual decrease in heart rate), the autonomic system possibly fails to return the blood pressure to baseline during phase II, thus, resulting in hypotension, and later in syncope.
1 Cox SV, Eisenhauer AC, Hreib K (October 1997). ""Seinfeld syncope"". Cathet Cardiovasc Diagn 42 (2): 242. doi:10.1002/(SICI)1097-0304(199710)42:2<242::AID-CCD41>3.0.CO;2-M.
2 Braga S., Manni R., and Pedretti R. (August 2005). "Laughter-induced syncope". The Lancet 366 (9483): 426–426.