Acute Coronary Syndrome (ACS): This is the most likely diagnosis due to the classic symptoms of squeezing chest discomfort, diaphoresis, and fatigue, which are commonly associated with myocardial ischemia or infarction.

Stable Angina: Although the symptoms can be similar to ACS, stable angina typically occurs with exertion and is relieved by rest. However, it's a consideration if the patient's symptoms are chronic and stable.
Pulmonary Embolism (PE): While PE can cause sudden onset of chest discomfort and shortness of breath, diaphoresis and fatigue are also common symptoms, making it a plausible diagnosis.
Pneumonia or Pneumonitis: Infections of the lung can cause chest discomfort, diaphoresis, and fatigue, especially if there's an associated pleuritic component.

Aortic Dissection: A life-threatening condition that can present with sudden, severe chest discomfort, which may be tearing in nature. Although less common, missing this diagnosis can be fatal.
Pulmonary Hypertension Crisis: A rare but critical condition where there's a sudden increase in pulmonary artery pressure, leading to right heart failure. Symptoms can include chest discomfort, diaphoresis, and fatigue.
Cardiac Tamponade: Accumulation of fluid in the pericardial space can compress the heart, leading to impaired filling and symptoms such as chest discomfort, diaphoresis, and fatigue.

Esophageal Spasm or Rupture: Although less common, esophageal conditions can mimic cardiac symptoms, including chest discomfort and diaphoresis.
Hypertrophic Cardiomyopathy: A condition where the heart muscle becomes abnormally thick, which can lead to obstructive symptoms and potentially cause chest discomfort, diaphoresis, and fatigue, especially with exertion.
Mitral Valve Prolapse: While often asymptomatic, in some cases, it can lead to chest discomfort, palpitations, and fatigue, especially if there's significant mitral regurgitation.