Worried about DVT from flying...?

I flew today on a 2 hour flight and heard a pop in my leg, when I got home there was a red bruise unlike no bruises i've had before. So I called NHS direct who sent me to get checked at the hospital who told me it just looks like a bruise and that I'm not in the high risk group so not to worry. But also they said if I get any chest pain or cough up blood to go back immediately. So I went home but I can't stop getting panic attacks making me think I'm getting chest pains. I just wondered if anyone could give me any advice to help calm me down? I was made to feel a bit stupid for getting it checked and it seemed like she was implying I must have bruised it before the flight but I definitely felt it pop and there was nothing there before flying! Am I being stupid?