Is a sudden collapsed lung bad and can you die from it?

Yes. If the pneumothorax creates enough pressure, it can compress the right side of the heart. This decreases the blood return to the heart. Without adequate blood return, your heart does not have enough blood to pump out to your body. This can be rapidly fatal.
Yes and Yes. A collapsed lung (pneumothorax) can occur following chest trauma or spontaneously, usually associated with an underlying weakness in the lung (bleb). Left untreated, pressure within the chest cavity can compress the flow of blood to and from the heart, which can be life-threatening. Thankfully, this can be easily treated by placing a chest tube into the affected chest cavity.
Possible. Can be life threateningtension pneumothorax is life threatening emergency if not treated fast and.