They are normally just another form of either a PAC or
PVC, the forceful beat is the heart making up
for the one that was dropped as it pushes the blood through the arteries. The current or tiny shock feeling is common, I have it, it is a form of adrenaline rush due to fear. I have had them in my head as well, they are called "head zaps" and are due to anxiety.
Anxiety is awful, and it is a vicious circle, the skips can cause the anxiety, and the anxiety can cause the skips.