My sister had/has epilespy, diagnosed as just a "seizure disorder" for the latter part of her teens and the early part of her twenties. I still remember being rather young and her having seizures at odd moments. Most frightening was at dinner one time, and her head started twisting to the right, she just said in a bit of a panicked tone "Mom, I'm having a seizure..." We all got up and helped her to the floor and got a pillow for her head.
First one she had was at school, I believe she was in 7th or 8th grade. I was in 5th. It's really scary at first...but sadly you get used to it and just do your best to be prepared.
She couldn't get her divers license for a while because of it, but with medication it came under control. A good neurologist and the proper treatment can make the world of difference, so as was said, insurance is a good thing. I never would mess around or get lax with issues of the brain. My sis hasn't had a seizure in a long long time thankfully. I'm glad that time has passed, but none of us forget.
I'm sorry you had and your friends had that shock and that Megan has this experience. As far as the actual causes, that's still widely discussed and researched. There's evidence for genetic links and evidence for it being random or environmentally caused. I'm not certain, I stopped reading up on it after it stopped being a part of my life.
Best of luck to her man, it's very important to have a support system that knows the issue and can handle it when she's most vulnerable.