Bam Im so sorry that your feeling this bad. Its hard to quit one thing, let alone caffeine and chocolate as well. Stress can also cause palpitations and heart problems. And I have panic attacks that cause palpitatioins all the time. I am on a high dosage anti depressant which I don't abuse cause it doesn't make me feel high, just normal. I used to be afraid to go to work, drive, or even leave the house. I know that not wanting to be around people at work is one of the symptoms that I have dealt with as well.
Its especially hard to not have stress if the doctors can't assure you that nothing is wrong with you. There may be nothing wrong with you at all, but for me I always needed everything checked before I would believe them. I hope that the doctors can hurry up and let you know whats going on, or whats not going on.
Hugs
Amy