If you're like us and value your sleep, you probably nodded off into your Ambien dreamland before the party started on post-prime time TV. Don't worry; we've got you covered. Here's the best of what happened last night on late night.

This is pretty big news, considering the history of "The Tonight Show." Jimmy Fallon was doing his monologue Tuesday night, and after telling a joke about Bernie Sanders, he faked an injury and asked for someone to "tag in" for him. Enter ... Jay Leno! Jay infamously battled both David Letterman and Conan O'Brien for the "Tonight Show" desk, but at least he and Fallon are still apparently on good terms. Jay must miss telling jokes on network TV at 11:30, since that was his thing for so long.

Lady Gaga was on "The Tonight Show" Tuesday night, although she didn't do one of the fun games. (She should've done Wheel of Musical Impressions!) Here she is talking to Jimmy Fallon about her favorite shows, including "Dateline" (?) and "Snapped." She went to acting school for almost 10 years, but she was terrible and awkward at auditions and couldn't get a job so she became a singer. She also discussed doing the Polar Plunge in Chicago with fiance Taylor Kinney, showed off her huge engagement ring rock, and explained her blood-drinking narcissist character in "American Horror Story: Hotel," which premieres tonight.

Bill Clinton -- aka Secretary of Explaining Stuff -- explained why Bernie Sanders and Donald Trump are doing so well. Here's part of his conversation with Stephen Colbert: Ronda Rousey made herself even more fans when "Geeking Out" over video games, talking about her long history with Pokemon, World of Warcraft and other games.

"The Late Late Show" keeps having too much fun, and here are "The Vampire Diaries" alum Nina Dobrev and former SNL-er Chris Parnell doing a game called "Pile High Club." The celebs should've been the ones forced to hold all that crap! Eric Stonestreet talked to Jimmy Kimmel about "Modern Family" NOT winning the Emmy, after winning five years in a row. He also shared his latest prank on co-star Jesse Tyler Ferguson. The prank was just earlier tha day and Jesse didn't even know yet. Eric grabbed Jesse's phone and "liked" a bunch of female butt twerking videos so everyone could see. Ellen Page, still promoting "Freeheld," offered a stand-up audition for "Conan," complete with a very professional hairbrush mic. Rose McIver of "iZombie" was on JKL and talked about her character eating the brain of a magician on the show. So she showed off a cool card trick: Rooney Mara talked about her "crying tent" on the set of "Pan" and how she almost got that living saint Hugh Jackman to snap.

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