I had something similar happen a while back but I was drinking an energy drink. My heart would start pounding and I almost felt a little nauseous. So i then went to a doctor to see if he could tell me what was wrong. After some testes It was deduced that I have random anxiety attacks. I m not saying thats what you have but these attacks are caused by stress, depression and an overwhelming amount of pressure from things and ppl around (health, work ie.) Look up the symptoms for anxiety and see if you fit. They can be triggered by lots of sugar and or caffeine.....