It depends from person to person. Some don’t get much warning if any. They just drop. Others can tell when it’s coming and/or have warning signs they can learn. A book I read as a kid had a character who heard a train horn getting louder as the seizure came on.

Just because you can tell it’s coming doesn’t mean it’s a good idea to drive, though. Maybe you won’t get a warning next time. Maybe you’ll get stuck in traffic where you can’t pull over safely. Your faculties are already starting to go when a seizure starts to come on, maybe you’ll have poor judgement about how far you can make it before you have to stop. Maybe you’ll stop, but you won’t be good to drive when you wake up again.