Can a collapsed lung happen again spontaneously?

Yes: About 20% of the time unless excission of blebs/bullae, abrassive/talc pleurodesis is done. After first spontaneous pneumothorax cat scan thorax advised to assess extent, number, size of blebs or bullae. If non smoker, apical congenital blebs may be the cause.Maneuvers that can apply sudden compressive or decompressive force to the thorax may cause blebs to rupture.Diving, skydiving, piloting aircraft.

Yes it can: A spontaneous pneumothorax, collapsed lung, is caused by a small bubble, bleb, that developed in the lung and has popped thereby leaking air. It is similar to a balloon popping. The first line of treatment is to place a chest tube in the chest cavity to remove the air. If the leak in the lung seals the tube can be removed. There is approximately a 50% chance it could recur again.

Yes: First recurrence is most common between 6 months and 3 years. Published 5yr first recurrence rates for primary spontaneous pneumothorax are around 20-30+%. For secondary spontaneous pneumothorax, 5yr first recurrence rate is around 40+%.