Hey nazim, like you I was driving home after work n stopped at a set of lights n bam I got my first attack, my heart felt like it missed a beat ( but felt like it stopped) I lost my breathe, and ever since then these thoughts of dying won't leave my head! I do have days where I'm fine but when I think " oh I havnt had ne of these thoughts for a while" bam it starts again n I get worked up about dying, when where how! Don't be frightened to talk to your doc because it made me feel like a huge weight was lifted from me! I'm a strong person who is a happy go lucky but with this going on, I'm not me, I'm 26 and the last time I went to the docs was when I was 11! So be honest and talk about it to your love ones, there's lots of us here who suffer the exact same as you, n ur not alone! Also I bought Bach rescue remedy and it worked wonders for me! Stay strong m8
The best thing is to go back to your doctor and discuss this with him/her. You obviously need more help and that could come in the form of a psychologist teaching you cognitive behavioral therapyand/or a psychiatrist prescribing you medication to combat the anxiety, something in addition to the Xanax that you already have.
In the mean time, try this breathing exercise. Take a deep breath in through your nose and hold it for 5 seconds, then let it all out through your mouth. Do this for several minutes until your heart beat is back to normal. It is possible to hyperventilate without knowing it so this is why the breathig is key. There are many meditation videos you can find on the web that you can also practice.
This is something that is very, very treatable and with the right help you will be back to the way you used to be so hang in there and get the professional help you are going to need to get over this.