Gastroesophageal Reflux Disease (GERD): The patient's symptoms of mild chest pain localized to the left side or medial chest, combined with a history of heavy alcohol use, suggest GERD as a likely cause. Alcohol consumption can exacerbate GERD symptoms.

Costochondritis: This condition, characterized by inflammation of the cartilage that connects the ribs to the breastbone, can cause chest pain that may be exacerbated by stress and can be localized to the left side or medial chest.
Musculoskeletal Chest Pain: Given the patient's recent job changes and high stress levels, musculoskeletal pain due to tension or strain in the chest muscles is a plausible explanation for his symptoms.
Alcohol-Related Cardiomyopathy: Although less directly related to the chest pain, the patient's heavy alcohol use puts him at risk for cardiomyopathy, which could potentially lead to chest pain among other symptoms.

Acute Coronary Syndrome (ACS): Although the patient is relatively young and his blood pressure and heart rate are within normal limits, it's crucial not to miss ACS, as it can present atypically, especially in younger individuals or those with risk factors such as heavy alcohol use and nicotine consumption.
Pulmonary Embolism (PE): While the patient's symptoms do not strongly suggest PE, it is a condition that can be deadly if missed. The absence of typical symptoms such as dyspnea or tachycardia does not rule out PE entirely.
Aortic Dissection: This is a life-threatening condition that requires immediate attention. Although the patient's presentation does not strongly suggest aortic dissection, any chest pain, especially if severe or tearing in nature, warrants consideration of this diagnosis.

Pericarditis: Inflammation of the pericardium can cause chest pain that may be sharp and can radiate to the left side of the chest. It is less common but should be considered, especially if the patient has recently had a viral illness or if there are signs of systemic illness.
Esophageal Spasm: This condition can cause chest pain that mimics cardiac pain but is related to abnormal esophageal contractions. It is less common and might be considered if other diagnoses are ruled out and the patient's symptoms persist.