Sounds like you have an arrhythmia, that is your heart has a conduction loop that causes it to beat irregularly and it looks like this occurs spontaneously. When your heart begins beating very fast, it ends up not filling with blood properly so not enough blood does gets pushed to the rest of the body. Since your brain does not get enough blood during these episodes, you faint. Chances are this is Wolff-Parkinson-White syndrome. This is pretty common and not frequently a cause of death. In fact, it came up on Modern Family (the mom has it).
Do you feel your heart start to race just before you pass out? Overall, your doctor's note indicates that it's not a structural issue, which is a huge relief. If you're a generally healthy guy, you should take a deep breath and realize that the smoking/obesity/high salt diet of many of your fellow Americans and ISH-ers will kill you much faster than your arrhythmia and that you'll be just fine. Hope you feel better, bro!