Vasovagal Syncope: This is the most common cause of syncope in children, often triggered by stress, pain, or fear, and can be preceded by dizziness, nausea, and abdominal discomfort. The patient's symptoms of dizziness before falling, headache, and abdominal tenderness are consistent with this diagnosis.

Orthostatic Hypotension: This condition can cause dizziness and fainting due to a sudden drop in blood pressure when standing up. The patient's symptoms of dizziness before falling could be related to orthostatic hypotension.
Migraine: Although less common in children, migraines can cause dizziness, headache, and abdominal tenderness, which are all present in this patient's symptoms.
Anxiety or Panic Disorder: These conditions can cause physical symptoms such as dizziness, headache, and abdominal discomfort, which may be contributing to the patient's pre-syncopal episodes.

Cardiac Conditions (e.g., Long QT Syndrome, Hypertrophic Cardiomyopathy): Although less likely, cardiac conditions can cause syncope and are potentially life-threatening if missed. A thorough cardiac evaluation is necessary to rule out these conditions.
Intracranial Hemorrhage or Mass: Although rare, an intracranial hemorrhage or mass can cause headache, dizziness, and syncope, and is a potentially life-threatening condition that must be considered.
Abdominal Conditions (e.g., Appendicitis, Intussusception): The patient's abdominal tenderness on the left side could be indicative of an underlying abdominal condition that requires prompt attention.

Pheochromocytoma: A rare tumor that can cause episodic hypertension, headache, and syncope.
Autonomic Dysfunction: A rare condition that can cause orthostatic hypotension, syncope, and other autonomic symptoms.
Mitochondrial Disorders: A group of rare genetic disorders that can cause a range of symptoms, including syncope, headache, and abdominal discomfort.