Vasovagal Syncope: This is the most common cause of syncope in young, healthy individuals. It is often triggered by stress, pain, or prolonged standing, leading to a sudden drop in blood pressure and heart rate, resulting in a brief loss of consciousness.

Dehydration: Severe dehydration can lead to a decrease in blood volume, causing a drop in blood pressure and resulting in syncope.
Anxiety or Panic Attack: Intense anxiety or a panic attack can lead to hyperventilation, causing a decrease in carbon dioxide levels in the blood, which can result in syncope.
Orthostatic Hypotension: A sudden change in position can cause a drop in blood pressure, leading to syncope, especially if the individual is not accustomed to standing for long periods.

Cardiac Arrhythmias (e.g., Supraventricular Tachycardia, Ventricular Tachycardia): Although less common in young, healthy individuals, cardiac arrhythmias can be life-threatening if not promptly diagnosed and treated.
Pulmonary Embolism: A sudden onset of syncope, especially if accompanied by chest pain or shortness of breath, could indicate a pulmonary embolism, which requires immediate medical attention.
Aortic Dissection: Although rare, an aortic dissection can cause syncope due to a sudden drop in blood pressure or cardiac output and is a medical emergency.

Subclavian Steal Syndrome: A rare condition where there is a stenosis or occlusion of the subclavian artery, leading to a reversal of blood flow in the vertebral artery, which can cause syncope.
Hypertrophic Cardiomyopathy: A genetic disorder that can cause the heart muscle to become thickened, leading to obstructive symptoms and potentially syncope, especially during exertion.
Long QT Syndrome: A rare genetic disorder that affects the heart's electrical system, potentially leading to life-threatening arrhythmias and syncope.