Yes, suffered approx 3 years ago with a Spontaneous Pneumothorax - This is not as uncommon as you may think and can happen to anybody, a small tiny defect in the lung wall can tear, sometimes though something as simple as coughing or a chest infection.
Many dont require specific treatment and will sort thenselves out, but I spent 4 days in hospital with a drain in my chest because I am asthmatic also. The chances of reoccurance are high in the first 6 months and I am sure you have been advised not fly in this period, but after 6 months and 12 months respectivley the changes of reoccurance drop dramatically.
I was back playing within 4 weeks, which is quite quick, just took it easy, My consultant was really supportive, the only concern was that if I played so hard that i ended up gasping for breath this could put unnecssary pressure on the newly healed lung. Since then never had any further problems.
An attack of Pneumothorax can be very painful! If it is a severe attack, you may even have to be admitted for an "aspiration" procedure to be done in hospital by way of insertion of a needle into the chest cavity to remove the trapped air. Were you by any chance a heavy smoker?
You may want to consult with a specialist for a breathing exercise regimen that is specific for this condition.