Curiouser & Curiouser - S2-E22
Trivia: All the sets in the dream sequence, particularly Nick's loft, are filled with props referencing Lewis Carroll's Alice in Wonderland books. They include white rabbits, flamingos, walruses, a squeaky-toy caterpillar - even a half-eaten piece of cake in Nick's fridge. The episode also has several background extras in Wonderland-style costumes, and numerous other references to the books, such as Nick literally falling through the looking glass at the end.
Answer: Nick was sick and tired of being an immortal bloodsucker. He wanted to be human, fall in love, get married, have children, grow old and die. As for Janette, according to her, she fell in love and the passion she felt "cured" her of her blood lust.