I did not have any indication. I worked from home and did a lot of sitting but I don't know if that mattered. I stood up to take a break one day and my leg hurt as if I had stepped in a small hole and twisted it badly. I thought it would pass but ended up going the doc who sent me immediately to the ER for tests. There were actually two clots. One ran from. My ankle to just under my butt and the other from the back of my knee up further. I was in the hospital for week. I am on a blood thinner all the time