I think the message that Lama Zopa wanted to send is that, however our karma manifest in our life, whether we get sick, we lost all our wealth etc... we should always continue our Spiritual practice because the difficulty we face now, is nothing compared to what it will be without spirituality. It is through Dharma and applying the methods through wisdom will we eventually be liberated from the suffering of this world.
So, yes, if getting sick will make us think more about practicing spirituality, then that would be our good karma... perhaps there was nothing else that would have moved us to this direction except being sick. After all, we have countless of karmic seeds both good and bad... perhaps through one's fortune, the bad seed was forced into ripening at a time when he/she will then lead a spiritual life due to that situation.
On the other hand, if I hit the jackpot, people may say that is my good karma. But if it takes me closer to dharma and use the money for positive actions, then yes good karma. But if the wealth makes me more attached, more desirous, less spiritual... then the money is the cause of my downfall and obtaining such wealth is due to bad karma.