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

Dehydration: Inadequate fluid intake or excessive fluid loss can lead to hypovolemia, causing a decrease in blood pressure. This is a common and easily treatable condition that can lead to presyncope and syncope.
Anemia: Low hemoglobin levels can reduce the amount of oxygen being delivered to tissues, including the brain, potentially leading to symptoms of presyncope.
Orthostatic Hypotension: A drop in blood pressure that occurs upon standing, which can be due to various factors including dehydration, medication side effects, or autonomic nervous system dysfunction.

Cardiac Conditions (e.g., Hypertrophic Cardiomyopathy, Long QT Syndrome): Although less common, cardiac abnormalities can lead to life-threatening arrhythmias and must be considered in the differential diagnosis of syncope.
Neurological Conditions (e.g., Seizure Disorders): While less likely, certain neurological conditions can present with symptoms mimicking presyncope or syncope.
Infectious Diseases (e.g., Septic Shock): Infections leading to septic shock can cause a severe drop in blood pressure, which is life-threatening and requires immediate intervention.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodes of high blood pressure but also lead to orthostatic hypotension.
Autonomic Dysfunction: Disorders affecting the autonomic nervous system, such as dysautonomia, can lead to blood pressure dysregulation and symptoms of presyncope.
Endocrine Disorders (e.g., Adrenal Insufficiency): Certain endocrine conditions can affect blood pressure regulation and lead to symptoms of presyncope or syncope.