Seize the Day

Applejack has been able to hide it from her friends for this long, but it's not exactly something she can control, so they might find out anyways.

Applejack suffers from epilepsy, meaning that she suffers from periodic seizures. Doesn't seem that bad, right? Well, to her that means weakness, and she refuses to show weakness, no matter the cost, even if she pushes the boundaries of her own element.