Allergic Rhinitis or Asthma Exacerbation: This is the most likely diagnosis given the exposure to molds, which are common allergens that can trigger or worsen respiratory symptoms like chest tightness in susceptible individuals.

Hypersensitivity Pneumonitis: An immune system disorder that occurs in some people after inhaling certain substances, including mold. It can cause chest tightness among other symptoms.
Infectious Diseases (e.g., Fungal Infections): Certain molds can cause infections, especially in immunocompromised individuals, leading to symptoms that might include chest tightness.
Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: If the patient has pre-existing COPD, exposure to molds could exacerbate symptoms, including chest tightness.

Pulmonary Embolism: Although less likely related directly to mold exposure, pulmonary embolism can cause sudden onset of chest tightness and is a potentially life-threatening condition that must not be missed.
Acute Coronary Syndrome: Chest tightness can also be a symptom of heart conditions such as myocardial infarction. While not directly related to mold exposure, it's crucial to consider in the differential diagnosis due to its severity.
Anaphylaxis: A severe, life-threatening allergic reaction that can occur rapidly and requires immediate medical attention. It could be triggered by mold exposure in highly sensitive individuals.

Mold-Induced Hypersensitivity Vasculitis: A rare condition involving inflammation of the blood vessels that could potentially be triggered by mold exposure, leading to a variety of symptoms including chest tightness.
Idiopathic Pulmonary Fibrosis: A condition in which the lungs become scarred, potentially worsened by environmental exposures including molds, though the direct link is less clear and would be considered rare in the context of acute chest tightness.
Occupational Asthma: If the mold exposure is work-related, this could be a consideration, especially if symptoms improve away from work and worsen upon return.