Pneumonia: This is a common condition that can cause worsening dyspnea (difficulty breathing) and chills, especially in the context of a respiratory infection. The combination of these symptoms, possibly accompanied by cough, fever, and sputum production, makes pneumonia a leading consideration.

Acute Bronchitis: While often less severe than pneumonia, acute bronchitis can cause significant dyspnea and may be accompanied by chills, especially if there is a significant inflammatory response or if the condition progresses.
Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: Patients with COPD can experience worsening dyspnea during exacerbations, which may be triggered by infections or air pollutants. Chills could accompany an infectious exacerbation.
Asthma Exacerbation: Similar to COPD, an asthma exacerbation can lead to worsening dyspnea. While chills are less common, they could occur if the exacerbation is triggered by a respiratory infection.

Pulmonary Embolism (PE): Although less common, PE is a critical diagnosis that must not be missed due to its high mortality rate if untreated. Dyspnea is a key symptom, and while chills are not typical, they could occur in the context of a post-operative or post-traumatic PE.
Sepsis: Sepsis, particularly when originating from a pulmonary source (e.g., pneumonia), can cause both dyspnea and chills. Early recognition is crucial due to its high mortality rate.
Cardiac Conditions (e.g., Myocardial Infarction, Heart Failure): Certain cardiac conditions can present with dyspnea and, less commonly, chills, especially if there is an infectious component or significant systemic response.

Pulmonary Vasculitis: Conditions like Wegener's granulomatosis can cause dyspnea and systemic symptoms including chills, but these are less common and typically accompanied by other specific findings.
Lymphangitic Carcinomatosis: This rare condition, involving metastatic cancer spreading to the lymphatics of the lung, can cause dyspnea. Chills could be present if there is an associated infection or systemic response to the cancer.
Eosinophilic Pneumonia: A rare condition characterized by eosinophilic infiltration of the lungs, which can cause dyspnea and possibly chills if there is a significant systemic inflammatory response.