Have you been under a lot of stress lately? Back when I was a soph in college I started having episodes where I would get dizzy, nauseous and would pass out cold. They performed tests on my heart and my blood sugar and everything was normal. Then just last year, I came home from work after picking up my daughter from her grandmothers, and started to have symptoms of a heart attack. I went to the ER and they told me the same. No irregularities. They started treating me for anxiety and I haven't had another episode since. I pray that you find answers, so that you can work towards fixing the issues. It's a scary place to be, when you know something is wrong but have no idea what is wrong.