Anemia: This is a common condition in adolescent girls, especially those with heavy menstrual periods. Anemia can lead to symptoms of dizziness and fatigue due to a decrease in the number of red blood cells or the amount of hemoglobin in the blood, which reduces oxygen delivery to tissues and organs.

Dehydration: Inadequate fluid intake or excessive fluid loss can cause dehydration, leading to dizziness and fatigue. This is particularly common in teenagers who may not drink enough water or engage in strenuous physical activities without proper hydration.
Vasovagal Syncope: This condition is characterized by a sudden drop in heart rate and blood pressure, leading to reduced blood flow to the brain and causing dizziness or fainting. It can be triggered by stress, pain, or prolonged standing.
Hypothyroidism: Although less common, hypothyroidism (an underactive thyroid gland) can cause fatigue, dizziness, and other symptoms. It's essential to consider this diagnosis, especially if other symptoms like weight gain or hair loss are present.
Nutritional Deficiencies: Deficiencies in vitamins like B12 or iron can lead to fatigue and dizziness. These deficiencies can be due to inadequate diet, especially in individuals with restrictive eating patterns or certain dietary preferences.

Cardiac Conditions: Certain heart conditions, such as arrhythmias, cardiomyopathy, or congenital heart defects, can cause dizziness and fatigue. These conditions are potentially life-threatening and require immediate medical attention.
Diabetes: Both type 1 and type 2 diabetes can present with fatigue and dizziness, among other symptoms. Early diagnosis and management are crucial to prevent long-term complications.
Infections: Severe infections, such as meningitis or sepsis, can cause dizziness and fatigue. These conditions are medical emergencies and require prompt treatment.

Mitochondrial Disorders: These are a group of disorders that affect the mitochondria, often presenting with fatigue and a range of other symptoms. They are rare and usually have a genetic basis.
Adrenal Insufficiency: This condition, where the adrenal glands do not produce adequate amounts of certain hormones, can cause fatigue, dizziness, and other symptoms. It is relatively rare and can be life-threatening if not treated.
Multiple Sclerosis: Although rare in adolescents, multiple sclerosis (MS) can present with a wide range of symptoms, including fatigue and dizziness. MS is an autoimmune disease affecting the central nervous system.