There are no laws to prevent you from owning a gun in Missouri, based upon a medical condition, as far as I know. I am not a lawyer either, but I do teach CCW classes and have never run across any such laws. As far as Missouri state law for CCW goes, it is just as Glock36 said. Mental health issues are addressed, but nothing about medical conditions. Of course, the Sheriff of the county in which you reside can deny your CCW application based on any information he may have that would cause him to believe you are a danger to yourself or others.
And your medical condition could certainly be a deciding factor on how and when you carry. That would be for you alone to determine. Just what triggers these seizures, (if known), the severity and length of the seizure, would be something to take into consideration. It probably would'nt be desirable to be rushed into an ER with a .45 in your waistband.