What you are experiencing is a loss-of-consciousness, unknown etiology.
The problem could be neurological, or circulatory. Yes epilepsy may be the reason.
It is likely to happen again, and you may be driving with a loved one inside the vehicle.
Needless to say you need a complete neurological work-up. As of yesterday. And if it happens again, an immediate trip to the ER.
There a few reasons you could be blacking out, it could be related to a large drop in blood pressure from time to time causing you to temporarily black out because your blood pressure is too low. It could also be related to epilepsy... you don't always have to present with the common 'fit' for it to be this, and often people suffering from epilepsy will just black out, there are many forms of epilepsy. It could also be related to other problems such as a head injury etc.
You should really see your doctor who can assess you, and may want to refer you for some tests. Your symtoms arn't specific enough for it to be diagnosed without assessment.
Regards, Dee.