Causes of Seizures (Not Epilepsy)?

I'm 19 and had a seizure back in November. I lost complete conciousness and according to witnesses, it was a grand mal seizure. After tests, my MRI and CT scan both came back clear…but my EEG came back slightly abnormal. I had gotten very little sleep the night before, which I know can cause seizures. The neurologist was unable to diagnose me with anything. I was on medication for a short period of time before stopping.

5 months later, I had another seizure. This one was completly unprovoked. The only two things that the seizures have in common was:
1. First time was in a fragrance lab, second time was in a mechanics shop (Strong odors?)
2. I regularly took protein shakes

Is it possible that either of these two similiarities caused the seizure, and if not, what else could have caused it (Im not epileptic, was not sick, and am not diabetic as far as I know)

Thanks!