I think..You have to think of it this way. The symptoms you described are what anyone smoking too much pot might experience, and most of those people do not have epilepsy. If you have any tendency to epilepsy because of your sister, it would take so much to bring it on heavy dose of pot that it would probably not be clinically significant. On the other hand, you should not be afraid to find out if you have any unusual sensitivity to epilepsy. Why don;t you get an EEG, and if there is any signs, it will forewarn about excessive behavior, and may prevent what you really don't want to happen.