Does dvt present symptoms most of the time?

So I have a terrible fear of getting a blood clot and dieting, and the strange thing is they don't run in my family, I have no risk factors, and have never had one. Ive had four ultrasounds on my legs and never had one. What scares me is the fact they can have no symptoms and you can just die. My doctors assure me that I would have pain and swelling, and that people usually do have symptoms they just ignore them till its to late. Can anyone help me alleviate this fear? If I did get one most likely would I have symptoms? I'm 23