Musculoskeletal Pain: This is often the most common cause of chest pain, especially when the pain is sharp and localized to one side. The fact that the pain started suddenly and the patient is unsure of any precipitating factors makes musculoskeletal pain a plausible explanation. Activities or movements that exacerbate the pain would support this diagnosis.

Gastroesophageal Reflux Disease (GERD): GERD can cause chest pain that is often described as burning and can be localized to one side of the chest. The pain can worsen after eating or at night, which might align with waking up in pain.
Pulmonary Embolism (less likely but considered due to the acute onset): Although less common, pulmonary embolism should be considered, especially if there are risk factors such as recent travel, immobility, or family history of clotting disorders. However, the lack of other symptoms like shortness of breath or cough makes this less likely.
Costochondritis: Inflammation of the cartilage that connects the ribs to the breastbone can cause sharp pains on one side of the chest, which could fit the patient's description.

Myocardial Infarction (MI): Although the patient is not taking any medications and the pain is localized to one side, MI is a critical diagnosis that must not be missed. The fact that the pain started suddenly and woke the patient up could be indicative of an MI, especially if there are underlying risk factors for heart disease.
Pneumothorax: A collapsed lung can cause sudden, severe chest pain that is often localized to one side. This is a medical emergency that requires immediate attention.
Aortic Dissection: This is a rare but life-threatening condition where there is a tear in the aorta. The pain is often severe and can be described as tearing or ripping, though it can also present as more localized chest pain.

Pneumonia: While pneumonia typically presents with fever, cough, and shortness of breath, it can occasionally cause localized chest pain, especially if the infection is localized to one area of the lung.
Lung Cancer: This would be an unusual presentation for lung cancer, which typically causes more systemic symptoms or symptoms related to the respiratory system, but it could be considered in the differential, especially in smokers or those with a significant smoking history.
Pericarditis: Inflammation of the sac surrounding the heart can cause chest pain that can be sharp and localized. It often improves with sitting up and leaning forward.