Vasovagal Syncope: This is a common cause of sudden dizziness and fainting in adolescents, often triggered by stress, pain, or prolonged standing. It's characterized by a sudden drop in heart rate and blood pressure, leading to reduced blood flow to the brain.

Orthostatic Hypotension: This condition occurs when there's a significant drop in blood pressure upon standing, which can cause dizziness and fainting. It can be due to dehydration, medication, or autonomic nervous system dysfunction.
Benign Paroxysmal Vertigo (BPV): Although more common in younger children, BPV can occur in adolescents, causing sudden, brief episodes of vertigo, often triggered by specific head movements.
Anxiety or Panic Attack: Anxiety and panic attacks can cause dizziness, lightheadedness, and a feeling of impending doom, potentially leading to falls.

Cardiac Arrhythmias: Conditions like supraventricular tachycardia (SVT) or long QT syndrome can cause sudden dizziness and fainting due to abnormal heart rhythms. These conditions can be life-threatening if not promptly diagnosed and treated.
Subarachnoid Hemorrhage or Other Intracranial Bleeds: Although rare in adolescents, these conditions can present with sudden onset of severe headache, dizziness, and loss of consciousness.
Seizure Disorders: Certain types of seizures, such as absence seizures or complex partial seizures, can cause sudden loss of consciousness or dizziness.

Multiple Sclerosis: This autoimmune disease can cause a wide range of neurological symptoms, including dizziness and vertigo, although it's relatively rare in adolescents.
Chiari Malformation: A structural defect in the cerebellum that can cause dizziness, vertigo, and balance problems, especially with certain head movements.
Inner Ear Disorders (e.g., Meniere's Disease): These conditions can cause vertigo, dizziness, and hearing loss, but are less common in adolescents.