I figured the headaches were his “real” sons wanting to come out and infect little Matthew

But OP grew up needing therapy to deal with his intense fear of water. And, from what his dad said, the instinct after that would just be to leave his family and move on to father more children like him. I think OP is doing the right thing in fighting against his primal nature to be something better. And I think it’s something we as human should also aspire to, to rise above our base nature and better ourselves, not only as individuals, but as a species ☺️