Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for severe breathing difficulty, fainting, confusion, or blue or gray skin.
And for anyone, someone who:
Seek urgent reassessment if chest pain or shortness of breath returns or worsens during recovery.
Follow-up usually includes a clinical review and repeat chest imaging.
The timing depends on the type of pneumothorax, treatment, symptoms, and local practice.
Keep scheduled appointments even if breathing feels normal, because symptoms alone cannot confirm that all pleural air has disappeared.
The article also says
Avoid smoking, including tobacco smoking.
Stopping reduces the risk of another spontaneous pneumothorax and supports overall lung health.
A clinician can discuss counseling and medicines used to help people quit.
Ask when it is safe to return to work, exercise, lifting, and sports.
Normal activity can usually be resumed gradually after recovery, but restrictions may be needed while symptoms or pleural air remain.
Contact sports and activities far from medical help may require additional planning.
Do not fly while a pneumothorax is still present.
British Thoracic Society guidance advises waiting at least seven days after a chest X-ray confirms complete resolution, although individual circumstances and airline rules may differ.
Recent surgery or underlying lung disease may require a longer delay.
Scuba diving carries a serious risk if trapped gas expands underwater or during ascent.
People with a history of spontaneous pneumothorax should not return to diving unless they have had specialist assessment and treatment considered sufficiently protective.
General medical clearance for exercise does not automatically mean that diving is safe.
Every sign above is quoted from the sofidex article on Collapsed lung. If you are not sure, err upward — it is always reasonable to be checked.