BCGosis or Disseminated BCG Infection: This is a rare but serious complication of BCG treatment, where the vaccine strain of Mycobacterium bovis disseminates and causes a systemic infection. The symptoms of fever, difficulty breathing, and hypotension could be indicative of a severe, disseminated infection, especially in an immunocompromised or elderly individual.

Pneumonia: Given the symptoms of fever and difficulty breathing, pneumonia is a plausible diagnosis. It could be community-acquired or hospital-acquired, depending on the context of the BCG treatment and the patient's recent history.
Sepsis: The combination of fever, difficulty breathing, and hypotension suggests a systemic inflammatory response, which could be due to sepsis. The source of sepsis could be related to the BCG treatment or an unrelated infection.
Tuberculosis (TB): Although BCG is used to prevent TB, it's possible that the patient has developed active TB, especially if the BCG treatment was for bladder cancer and the patient has a compromised immune system.

Septic Shock: A severe systemic infection leading to organ dysfunction, which would explain the hypotension and difficulty breathing. Prompt recognition and treatment are crucial.
Pulmonary Embolism: Could cause difficulty breathing and hypotension, especially in a patient who may have been immobile for a period following the BCG treatment.
Anaphylaxis: Although less likely given the time frame after BCG treatment, anaphylaxis is a life-threatening condition that requires immediate recognition and treatment.

Miliary Tuberculosis: A rare form of TB that is characterized by a widespread dissemination of TB bacilli through the bloodstream, leading to a miliary pattern on chest X-ray. It could explain the systemic symptoms.
BCG-induced Lupus: A rare condition where BCG treatment triggers systemic lupus erythematosus (SLE), which could present with a variety of systemic symptoms including fever, difficulty breathing, and hypotension due to autoimmune mechanisms.