Three years ago I developed a DVT in my right calf. I thought it was a strained muscle, but when I looked at my leg and saw it was slightly swollen, I went to the doctor. She sent me for an ultrasound, which came back clear; she diagnosed superficial clots which she said would dissolve on their own, and told me to take Advil.
I felt like I was waiting for the other shoe to drop. The pain went away, but came back a month later. Back to the doctor, another ultrasound, and they took me right over to the ER and put me on a blood thinner for six months. It took a while to kick in, so for a while I had to give myself stomach injections...no big deal, really, because the needles were tiny little things. I had been working out right up until the previous day, and the ER doctor told me that could have made my clot dislodge and go to my lung.
I had none of the risk factors for DVT; the hematologist said the closest he could come to pinpointing a reason for it was a folic acid deficiency. They did all kinds of expensive genetic testing to see if I had issues with clotting factors. Being on Warfarin was a pain...I had to go to the lab and have blood drawn regularly to check the meds level, and I couldn't eat green vegetables. I was told that I would need to go the ER immediately if I hit my head on anything.
Since then, I've read you should never settle for doctors' tendencies to blow off what they call superficial clots. If you're diagnosed with them, don't let them tell you Advil will fix it. I've read about people who died because of it.