The post from achillea addresses an important issue - and that is in times of anxiety there may be a surge of catecholamines (i.e. adrenaline). These catecholamines may act on specific receptors of the heart that are responsible for increasing heart rate, which may in turn, worsen and/or increase the number of premature beats (PVC, PAC's) that you already have. There are certain medications such as beta blockers that can be prescribed in the right clinical setting to help, but should be prescribed by a cardiolgoist/licensed physician if deemed necessary. If you have significant anxiety, you may also need to speak with someone about techniques of calming yourself down in certain situation and/or if other medications are indicated (anxiolytics, etc).
You sound exactly like me! Any kind of stress, good or bad feelings brings them on. Somtimes I too get them one right after another for hours. I try to redirect my mind to other thoughts and totally ignore them, but it is hard sometimes when I get 12 or 15 a min. My EP told me mine are unifocal and most likely coming from the left side of my heart. He scheduled me for a EP study and ablation, but I am taking verapamil and trying to just cope. Exercise seems to help with my anxiety I have over these PVC's.
Adrenaline, the stress neurotransmitter/hormone (you can google this), is released anytime you're feeling worried, stressed, anxious, whatever--even if you *think* that you're not being affected on a rational level.
And the thing about extra adrenaline is that is does increase extrasystoles, and it's worse for those who are sensitive enough to be aware of them.
When you have been given the cardiac all-clear by virtue of many tests, and you're still tormented both by increased extrasystoles as well as awareness of them, it's time to take yourself to a specialist who deals with the real problem: your emotional response to essentially harmless physical 'noise.'
Speaking from experience (lots of it), I strongly suggest one session with a good psychiatrist. This can actually give you your life back, allowing you to concentrate once more on the things that really matter.