 " Big Man on Hippocampus " is the tenth episode of the eighth season of the Fox animated comedy Family Guy . It originally aired on Fox in the United States on January 3 , 2010 . The episode features Peter after he suddenly begins suffering from amnesia , and can no longer remember anything about his life , including his own family and friends . His wife , Lois , then attempts to reintroduce Peter to his surroundings , but he soon discovers partying , and having sex with other women is much more entertaining . Frustrated , Lois decides to leave her husband , causing her neighbor , Quagmire , to attempt to win her over . 
