Hi mah,
I had my first pulmonary embolism last month. I was worried about this same exact thing; knocking the clot loose and sending it deeper into the lung. I was told that it was safe because the clot was at a "dead end." I still didn't use my vest for a few days just to be safe.
I'm interested in your experiences with having a PE. When I had a PE I passed out, woke up on the floor in a fetal position lying in a pool of blood with no idea what happened. My dad found me and kept saying "what happened!?" I looked down at the blood and said "it's not blood, it's raspberry jelly" (LOL, he had just made some homemade raspberry jelly that looks like blood, and I'd at some that morning). The blood was coming from a cut on my nose that I got somehow. It was very odd. I got blood everywhere, all over the floor, all over my vest (which was beside me), my laptop was on the floor beside me when it was sitting on my computer desk before... I still haven't been able to piece together what actually happened. I also somehow fractured my tailbone, one of my end plates, one of my vertabrae, my nose, and now I have compressed discs ;x