A person with a "normal" heart will generally generate a couple of PVC's after a second cup of coffee. As yarrow stated, some people are more sensitive to these events. If your cardiologist says "don't worry about them", don't worry.
On one of my 24-hour Holter monitors, 4800 PVCs were recorded. That is considered such a low number as to be boring. Many on this board have been clocked at more than 10,000 in a 24-hour period.
The thing is that every normal human--every single one--has PVCs or some other form of ectopic beat at times, BUT only the hypersensitive among us are aware of them.
And your heart isn't really stopping, although it feels as though it is. What's happening is that you have an early small contraction that is so tiny that you don't even feel it. This is the 'Premature' ventricular contraction. Then there's a very small delay until the next normal beat, and during this time the heart--which is elastic--gets a chance to fill up a bit more than usual. To pump out this slightly larger amount of blood, the heart contracts more vigorously, which only makes sense. This delayed beat you (and I) really feel: It's a big BOOM to us.
But that's all that's going on. The heart never stops beating in one of these episodes. It's all a matter of timing.