should I be going to doctor? or hospital?

Hi. I'm 21 years old. The past few years, I have been having something strange happen, about once a week. Without warning, it will feel as if my heart is beating very hard, and it feels as if it jumps up into my throat. I will have difficulty breathing, and begin coughing and feeling dizzy. It only lasts about 30 seconds, but when it happened today, I was driving and almost swerved off of the road. I can't seem to find any connections. It has never happened when I am working out, to the best of my knowledge. It often happens if I am just walking or sitting, but never during heavy excercise. I have mentioned it to the college doctor before, and they shrug it off as nothing. However, I almost passed out today, and I can't help but think something is wrong. But, it only happens about once a week...What could it be, and what should I do? I am starting to get worried..

I've tried to talk to the doctor about it, and they pretty much just roll their eyes and talk about stress at me...So, they could tell if I had an abnormal heart beat within the past few hours?

Yes, they can tell if you have had an irregular heart rhythm by doing an EKG, or Halter Monitor (some 24-48 hours).  Perhaps doctors have rolled their eyes as you are young.  Most dont expect younger people to have heart conditions...but, it happens.  It did to me. 

Do you have a family history of heart disease?  This will increase your odds of having a heart condition.  Drinking, smoking, diet, any number of things could be the cause of what is going on.  So basically you will not know until you just get a full work up done.