Does anyone know why I may have heart palpatations?

This morning I stretched and instantly felt my heart beat, looked down and WATCHED my HEART nearly jump through my chest, for about 50 beats.

Am I over training, lifting to heavy on my lifting days? Drinking too many sugar free red bulls (1 a day)?

I do not smoke, drink, or any of those really bad things, eat ok.... Run, bike, or Excercise 3-5 times a week, not over weight, 32 yo, 5'4, 137 lbs, what's up? Happened 2X..