White Coat Hypertension or Anxiety-Related Hypertension: The significant difference between the blood pressure readings at home (199/96) and in the ED (145/72) suggests that the patient's elevated blood pressure at home could be due to anxiety or stress, which is a common phenomenon, especially in young individuals. The episodes of dizziness could be related to anxiety or stress as well.

Essential Hypertension: Although less common in young individuals, essential hypertension could be a consideration, especially if the patient has a family history of hypertension. However, the significant variability in blood pressure readings makes this less likely as the primary cause.
Orthostatic Hypotension: The episodes of dizziness could suggest orthostatic hypotension, especially if the patient experiences a significant drop in blood pressure upon standing. However, the blood pressure readings provided do not directly support this diagnosis without further orthostatic vital sign measurement.
Anxiety Disorder: Given the potential for anxiety to cause both elevated blood pressure readings and episodes of dizziness, an anxiety disorder should be considered, especially if the patient reports other symptoms of anxiety.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodic hypertension and symptoms like dizziness, headaches, and palpitations. Although unlikely, missing this diagnosis could be catastrophic.
Hypertensive Emergency: Although the blood pressure in the ED is not severely elevated, if the patient's symptoms were due to end-organ damage from severely elevated blood pressure at home (e.g., hypertensive encephalopathy, cardiac issues), this would be a critical diagnosis not to miss.
Cardiac Causes (e.g., Arrhythmias, Cardiomyopathy): Certain cardiac conditions can cause both hypertension and dizziness. While less likely in a young individual without other symptoms, these conditions can be serious and require prompt diagnosis.

Renal Artery Stenosis: A rare cause of secondary hypertension, more commonly considered in patients with resistant hypertension or those with specific risk factors.
Hyperthyroidism: Can cause hypertension and symptoms like dizziness due to palpitations or orthostatic changes. However, other symptoms such as weight loss, exophthalmos, or heat intolerance would typically accompany it.
Coarctation of the Aorta: A congenital condition that can cause hypertension, typically diagnosed in childhood but could potentially present later in life if mild. It's an unlikely cause in this scenario without other suggestive symptoms or signs.