It is often the case that in the background of a successful comic, there has been tragedy. For Molly Shannon, it was surviving a 1969 car accident that killed her mother, younger sister and a cousin and left her father with a leg injury. "It's a massive loss that affects everything, but not consciously," she has said. Perhaps ironically, the perkily petite brunette with flashing blue eyes has become best known for her pratfalls and physical comedy on NBC's "Saturday Night Live", which she joined in early 1995. The Ohio native trained at NYU's Tisch School and briefly worked as a researcher for