Syncope is an abrupt loss of consciousness followed by a relatively quick recovery. The causes of syncope range from relatively benign to life-threatening. It is seldom overlooked and usually precipitates a visit to a medical professional. Syncope that occurs in or around the water poses particular challenges. Drowning often results when a diver loses consciousness and remains in the water. A rapid response is required to bring an unconscious diver to the surface and prevent death. Syncope can also occur upon exiting the water, due to such factors as exertion, dehydration and normal return of blood volume to the lower extremities. [ad:media]The initial response to syncope should focus on the ABCs of basic life support: airway, breathing and circulation. Advanced cardiac life support may be called for. Often, placing syncopal patients flat on their back in a cool environment will quickly restore them to consciousness. If syncope occurs following a dive, it is important to consider decompression sickness, pulmonary overinflation and immersion pulmonary edema in addition to the usual causes of the condition. Although both syncope and cardiac arrest result in a loss of consciousness, they can usually be clearly differentiated. The list of possible causes of syncope is extensive, but a good medical history can help eliminate the majority of them. The patient's age, heart rate, family history, medical conditions and medications are key in identifying the cause. If syncope is accompanied by convulsions (known as "tonic-clonic movements"), it may have been precipitated by a seizure. If it occurs upon exertion, a serious cardiac condition may be preventing the heart from keeping up with the demands of the physical activity; chest pain may be associated with this type of syncope. If standing up quickly results in syncope, that points to a cause known as "orthostatic hypotension." And pain, fear, urination, defecation, eating, coughing or swallowing may cause a variation of the condition known as "reflex syncope." A medical evaluation after an incident of syncope should include a thorough history and physical — plus interviews with witnesses who observed the individual's collapse and who can accurately relay the sequence of events. A few cases may require more extensive investigation, and some result in no conclusion.