Tuberculosis (TB): Fatigue and night sweats are classic symptoms of TB, especially in individuals with a history of exposure or those with compromised immune systems. The chronic nature of these symptoms aligns with the typical presentation of TB.

Lymphoma: Both Hodgkin's and non-Hodgkin's lymphoma can present with systemic symptoms such as fatigue and night sweats, often referred to as "B symptoms."
Chronic Infections (e.g., Endocarditis, Osteomyelitis): Chronic infections can cause prolonged fatigue and night sweats due to the body's ongoing inflammatory response.
Hypothyroidism: Although less common, hypothyroidism can lead to fatigue, and some patients may experience night sweats, particularly if the condition is severe or untreated.
Anemia: Severe anemia can cause fatigue, and in some cases, night sweats may occur due to the body's decreased ability to transport oxygen.

HIV/AIDS: The acute retroviral syndrome or the chronic phase of HIV infection can present with fatigue and night sweats. Missing this diagnosis could lead to delayed treatment and significant morbidity.
Malignancies (e.g., Leukemia, Advanced Cancers): Various cancers can cause these symptoms, and early detection is crucial for effective management and prognosis.
Sepsis or Septicemia: Although typically presenting with more acute symptoms, sepsis can sometimes manifest with fatigue and night sweats, especially in the early or subclinical stages.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodic symptoms including sweating, but night sweats and fatigue could be part of the clinical picture.
Brucellosis: A zoonotic infection that can present with non-specific symptoms such as fatigue and night sweats, particularly in individuals with occupational exposure to animals.
Whipple's Disease: A rare, systemic bacterial infection that can cause fatigue, night sweats, and weight loss among other symptoms, often mimicking more common conditions.