What should I do if a worshiper next to me falls due to illness or an epileptic seizure during prayer?

The basic principle is that it is forbidden to interrupt prayer except out of necessity, such as saving a life from destruction or harm, or securing property that is feared to be lost. It may even be obligatory to interrupt prayer to help someone in distress, rescue a drowning person, or extinguish a fire. In a case like that of a patient, it is obligatory to interrupt prayer to provide him with aid, unless someone else undertakes that task. Then, one should resume their prayer.