I'm not a medical expert, but I have read a good amount of medical books so take anything I say into consideration but with a decent sized grain of salt.
The primary active agent to my knowledge for energy drinks is caffeine. Like all stimulants it can force the body to perform at a higher level then it wants to based on its highly developed control systems. Your body's control systems do tend to sand bag, which is why military training involves redefining limits, but abusing that does have consequences.
WebMD drug fact entry. Your neck is connected to a lot of muscles in your back, but to the my limits knowledge would tend to imply the only way it should normally be able to effect the heart is through possibly limiting respiration. That brings up a whole host of questions. The Thyroid is in that area enough, albeit in the front, that movement might effect it which is the gland that controls metabolism and heart rate and could have been messed with by the caffeine. That could be a real factor, but I'm not qualified to state from a position of knowledge whether it would be or not.
These people however might.
I think it's probably best you go see a doctor ASAP. If the caffeine has caused a
irregular heart beat that's not something you want to leave alone, and a simple EKG should be easy enough to arrange.