Wow someone is definitely watching over you my dear, its very hard for people to find out they even have blood clots without a battery of tests. Thankfully they stayed in the lungs which was able to give you warning signs, but they could have easily moved to the heart or the brain. I know being on Warfarin or Heparin isn't the most pleasant thing to have to do but its better than the chance of having another round with them.
It's important for all to know when your on very long airplane rides - whether or not your in business or economy class you need to get up and move around the cabin. You need to help keep the blood flowing through the body or you run a risk of developing blood clots. There are numerous medical studies that have proven that the risk of getting blood clots during or after a flight is dramatically increased.