Adrenalin rushes.

[OakLeaf]

I get panic attacks occasionally. Up until this past year they were always the really mild kind that just felt like "adrenaline rushes." Here recently I've had a couple of the scarier ones - now I understand what people mean when they think they're having a heart attack, thinking they're about to die. Yikes. Panic attacks can cause palpitations all by themselves...

Reducing your overall stress level, through meditation or whatever, has got to help.