Here "overtake him" represents suddenly happening to him. Possible meanings are that "terrors" is a metonym for 1) things that cause people to be afraid. Alternate translation: "Terrifying things suddenly happen to him" or 2) fear. Alternate translation: "He suddenly becomes terrified"
The word "waters" refers to a flood. Floods can happen very suddenly when people do not expect them, and they are dangerous and frightening. Alternate translation: "like a flood" or "like waters that rise up suddenly" (See: [[rc://en/ta/man/jit/figs-simile]])