Pulmonary Embolism (PE) is caused by a blocked artery in the lungs. The most common cause is a blood clot that forms in a deep vein in the leg and travels to the lungs, where it gets lodged in a smaller lung artery. Almost all blood clots that cause pulmonary embolism are formed in the deep leg veins. It can cause low blood oxygen levels that can damage other organs in the body. A large PE or many clots can quickly cause serious life-threatening problems and, even death.
I've had a couple of these, one single and one bi-lateral (both lungs), and is quite scary finding it very difficult to breathe. Having one is not fatal, though it can be. Treatment is blood thinners which help dissolve the clot and prevent others from happening. My first was misdiagnosed as an asthma attack and didn't get properly treated for 5 days but, obviously, it didn't kill me. I was told I'd be on blood thinners for life but chose to stop my blood thinners on the belief mine was a freak occurrence and wouldn't happen again. The point I want to make is that when I told my Pulmonologist I stopped the blood thinners and was aware of the risk but I refused to spend the rest of my life in fear of another. He surprised me by saying "good for you!" and told me that most of his patients did spend their time sitting home fearing another.
Fifteen years later I had the bi-lateral PE's and felt I would die, again I didn't and was put back on blood thinners.