When do you run, have you eaten 3 hours before, could be low blood sugar I suffer from this a lot and snack regularly. I also have low blood pressure, have fainted on a number of occassions after crossing the line of races.
Try eating more salt to help raise your blood pressure before/after training. I have several doctor friends who say this explains why I crave salt, I tend to shock people with the amount I put on my foods!
