“Lord, have mercy on my son: for he is lunatick, and sore vexed: for ofttimes he falleth into the fire, and oft into the water.”
King James Version (KJV)
17:15 He is lunatic - This word might with great propriety he used, though the case was mostly preternatural; as the evil spirit would undoubtedly take advantage of the influence which the changes of the moon have on the brain and nerves.
Mt 17:15 My son; for he is lunatic. "Epileptic", in the Revised Version. The symptoms are those of epilepsy, in this case caused by demoniac possession. The son was a child (Lu 9:38). He was dumb as well as epileptic (Mr 9:18).