Apparently, you don't have much experience with civilian healthcare...

The right answer here is to go see a doc. Seeing a doctor who's familiar with treating members of the military will increase the likelihood of the doc actually being familiar with what might be going on, since military folks are more likely to push themselves to that point than civilians. If the doctor is military him/herself, it increases the likelihood of the doc being personally aware of the situation. In any case, blacking out isn't something to pass off as unimportant or a normal part of training.

A couple of examples: Friday, I went to my (civilian) doctor for a checkup. When the nurse did my vital signs, she became upset because my resting heart rate was "only" 52, way too low for what she thought was correct for a guy two months short of his 60th birthday. Another guy I'm aware of who's 65 and a lifelong runner and cyclist had a resting heart rate of 40, and his doc wanted to put in a pacemaker. Civilian docs aren't familiar with people who stay in shape, at least not to the extent that military docs are.