yes it can all be anxiety related. that's not to say it CAN'T be something else...there's ALWAYS something else that it can be...but the vast majority of the time, when all the symptoms point to anxiety and no tests indicate anything else, that's what it is. i take a beta-blocker called propranolol and it does help a lot with my heart palpitations caused by anxiety...but sometimes i still get a racing heartbeat or strong heartbeat...it just depends on the situation. so a beta-blocker isn't a gaurentee that you won't experience problems like that. quitting smoking is a very good idea because whatever problems you have, smoking certainly does do a number on your heart. somehow i was able to quit smoking in april. i was a nervous smoker...i smoked all the time to calm myself down, so i smoked a lot. there are actually some physical withdrawal symptoms that can last a while after quitting smoking. most people don't realize that. some people even experience acute pain that gets worse with time instead of better. this is something to consider. but since you've smoked for only 5 years, it's very unlikely that it has caused any form of cancer. it's not impossible...but it is VERY unlikely especially at your age. so all in all, are you getting treated for anxiety? because if that's what it is, you will certainly need more than just a diagnosis to get better. it will need to be treated.
you know allot of people come here with the same thoughts as you, the usual first step is to get a medical check up you have done that. Now I say to you, (from reading your post) stop playing Doctor, meaning stop self diagnosing yourself! I have seen way to many people could of gotten better in a shorter time, but went through the, 1) something physical must be wrong with me 2) need more test 3) self diagnosis. you may need a therapist to help you figure out what is going on in you that is telling your body there is DANGER, when in fact nothing NO DANGER, in the mean time work on deep steady breathing exercises it really can help you with the different "feelings" going through your body! My main concern in your post is toward the end when you said, , "That's what people are telling me but I find it hard to believe". I have seen people come here suffering and not wanting to take advice from people who have been there and are in different stages of beating this, but will not accept! so accept now it's anxiety and let the WORK start to getting back to a normal life again! keep posting. !