OntarioMike,
I agree with achillea's comments to you on this thread. Your diagnosis of anxiety, with panic attacks, is the cause of your presentation most likely. Panic attacks, along with the sense of impending doom, walls closing in, shortness of breath, and chest pressure, also include palpitations, which is due to the excessive sympathetic response (flight or fight) due to adrenaline in the blood. The palpitations can be just due to the heart beating stronger from the increased stimulation, or can actually be abnormal beats caused by the adrenaline over stimulating heart cells which then activate early or abnormally. Regardless, these will not make you "drop dead," and frankly, worrying yourself about it excessively just causes more anxiety and more adrenaline in the system, which will only increase your palpitation rate and severity.
Get the Holter monitor completed, follow up results with your physician, and get further testing if warranted based on what they find. If all findings are benign, and truly just anxiety related, then you should consider more intense evaluation and therapy for the anxiety and panic attacks which should help a lot.
You are a 29 year old man who does not complain of chest pain or sweating, so unless you have a lot of risk factors like a strong family history, high blood pressure, documented heart abnormalities, or obesity, nah, you're probably not going to drop dead any time soon, nor will your heart just stop.
It will help if you understand what goes on with benign ectopic heartbeats (which I am betting will be part of your diagnosis), so copy and paste this into your google search box:
kenyon cardiology/forums/backup/topic-24286.html
It's a good explanation by a knowledgeable guy named John Kenyon.
Being hyper-aware of these heartbeats is a curse for some of us (including me), so if you are diagnosed with 'nothing to worry about' and are still feeling very anxious about them, my advice is that a couple of visits with a good shrink will go a long way towards helping you to live with these things.