It's strange isn't it Alan, we are always told that clots start in the legs and move up to the lungs, but I had terrible chest/shoulder pain, couldn't breathe and went to my GP who listened to my chest and said there was nothing wrong.
3 weeks later I developed swollen painful calf and went back to GP who sent me straight to A&E. I got nuked at the same time and they discovered all the clots on my lungs that had been causing problems for weeks.
Miracle really that i'm still here, as the last lot hit the heart too.
It sounds to me as if yours was an undiagnosed DVT which moved onto lungs. Which anti coagulant are you on? I got lucky this time, as they have prescribed rivaroxaban instead of warfarin so I don't have to keep going for blood tests.