How long do you have to wait until you could do physical activity after a lung collapse?

Good question.: It depends on cause of pneumothorax and how it was treated, to give you some idea of chance of recurrence. If this was your first episode, it was probably treated with chest tube alone, and chance of recurrence is actually pretty high. Vigorous exercise, you should probably refrain for a few weeks. And quitting smoking will lessen chances too.

Varies : Depends on prexexisting situation and risk factors.. Older, emphysema, poor general condition can take several months. In a young otherwise healthy person 4-6 weeks may be enough. There is an incidence of recurrence which is an issue. Smoking is bad!

4-6wk: Usually, around 4-6wks. Depending cause of "collapsed lung" (pneumothorax). Spontaneous pneumothorax first recurrence rates depending on type ranges 20-40+%. Depending activity/lifestyle and cause (if one found), you may require surgical intervention / vats pleurodesis to prevent/decrease risk of further recurrence.