Acute Coronary Syndrome (ACS): Given the patient's age, family history of heart disease, and symptoms of mild chest pressure and dizziness, ACS is a highly plausible diagnosis. The alleviation of symptoms with raised legs could suggest a component of orthostatic hypotension, but in the context of chest pressure, ACS remains a primary concern.

Dehydration: The patient's symptoms of dizziness and lightheadedness, which improve with raising his legs, could indicate dehydration, especially considering the use of medications like omeprazole and 5ASA, which might contribute to fluid loss or electrolyte imbalances.
Orthostatic Hypotension: This condition is characterized by a drop in blood pressure upon standing, leading to dizziness and lightheadedness. The improvement with leg elevation supports this diagnosis, and it could be exacerbated by medications such as dexidrine.
Anxiety or Panic Attack: Although less likely given the chest pressure, anxiety or a panic attack could explain the dizziness, lightheadedness, and possibly the chest discomfort, especially if the patient is experiencing stress or has a history of anxiety disorders.

Pulmonary Embolism (PE): A potentially life-threatening condition that can present with sudden onset of chest pain and dizziness. Although less common, it's crucial to consider, especially given the patient's age and potential for immobility or other risk factors not mentioned.
Cardiac Arrhythmia: Conditions like atrial fibrillation can lead to decreased cardiac output, causing dizziness and chest discomfort. Given the family history of heart disease, this is an important consideration.
Aortic Dissection: A severe and life-threatening condition that can present with chest pain and dizziness. The absence of severe, tearing chest pain does not rule out this diagnosis, and it must be considered, especially in the context of a family history of heart disease.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodes of hypertension, tachycardia, dizziness, and chest pain. Although unlikely, it's a diagnosis that could explain the patient's symptoms, especially if they are episodic and associated with other symptoms like palpitations or sweating.
Thyroid Storm: Given the patient's use of synthroid, a condition of excessive thyroid hormone levels could potentially cause dizziness, chest pain, and other systemic symptoms. However, this would typically be accompanied by other signs of hyperthyroidism.