Gastroesophageal Reflux Disease (GERD): The patient's symptoms of coughing only at night, which occurs every year after getting a cold, suggest a possible link to GERD. Lying down can exacerbate reflux, leading to nighttime coughing. The absence of daytime cough and negative allergy testing support this diagnosis.

Postnasal Drip: Also known as upper airway secretion syndrome, this condition can cause coughing, especially at night when mucus drips down the back of the throat. The patient's history of colds leading to cough suggests this could be a contributing factor.
Asthma: Although the patient's symptoms are atypical for asthma (coughing only at night with no daytime symptoms), it's still a possibility, especially if the asthma is mild or exercise-induced. However, the lack of other symptoms such as wheezing or shortness of breath makes this less likely.
Chronic Bronchitis: This condition could be considered, especially given the patient's age and the recurrent nature of the cough. However, chronic bronchitis typically presents with a more persistent cough and possibly other symptoms like sputum production.

Lung Cancer: Although unlikely given the recurrent and seasonal nature of the symptoms, lung cancer can present with a cough. It's crucial to consider this diagnosis, especially in older adults, to ensure timely diagnosis and treatment if present.
Pulmonary Embolism: This is a less likely cause of chronic cough but is a critical diagnosis not to miss due to its potential for severe consequences. The presentation would typically be more acute, but it's essential to keep this in mind, especially if other risk factors are present.
Tuberculosis (TB): TB can cause a chronic cough, and although less common in some regions, it's a diagnosis that should not be overlooked, especially if the patient has been exposed or has risk factors.

Eosinophilic Esophagitis: This condition can cause a chronic cough, especially if associated with GERD. It's less common but should be considered if other diagnoses are ruled out and the patient continues to have symptoms.
Sarcoidosis: A systemic disease that can affect the lungs and cause cough among other symptoms. It's rare and would typically present with additional symptoms, but it remains a possibility in the differential diagnosis of a chronic cough.