My Son Passed Out While Driving - Blood Work Showed

My son passed out while driving - blood work showed no problems. the doctor suspected maybe a panic attack. He's 33 and it's been four months with no problem. The other day though he felt the symptoms again - an odd feeling in his guts and then it traveled up to his brain where he experienced a bzzz feeling. He pulled off the road and nothing further happened. He doesn't recall being stressed or overworked or anything. He does work an early shift at his job in a grocery store and is in a couple of bands. What do you think?