For what it's worth, if the doctors do find something, they will likely put your dad on medication that will help. I was diagnosed with epilepsy after having 2 seizures, 7 months apart, no apparent cause to them, and was put on medication. I also witnessed my mom having one, and I will fully agree with you, that they are frightening.
Fortunately, with people around, it sounds like your dad is being well taken care of, and that is the most important thing. There is another website with information -
www.Epilepsyfoundation.Org that you can check out. Or you can simply do a search on google or something. When I was first diagnosed, I found a lot of information on it this way, and through talking to a neurologist that was very helpful. Best of luck.