As someone who spent high school in close contact with a couple kids who had seizures, for starters I can say that the appearance is usually much more severe than the actual affect. In the cases of my friends, they weren't life-threatening in any real way (keep in mind, this could be different for Mary Kay, as no one knows what's causing them yet) other than the obvious possibility that they could hit their head on something on the way down.
Diagnosis and medication can be very tricky though. For one of my friends, the change in medication made the attack much less violent on the outside (instead of dropping like a stone and shaking, he'd slowly sink down and just lay there), but they later discovered it was having a much more severe effect internally.
Seeings as Rick is back with the team, I'd assume Mary Kay is not under any immediate threat. Hopefully the doctors can figure out the cause and square things away for her