Season 5, episode 24: "Now or Never"
We commend you if you survived through this roller coaster ride. Toeing the line between sweet and tragic, this episode begins with a cancer-stricken Izzie slowly losing her memory after brain surgery. Then things get a little lighter when Meredith and Derek confirm their love with a Post-It note wedding. Pretty cute, right? Then, a horribly disfigured George spells out 0-0-7 on Meredith’s palm and your heart dropped into your stomach. The episode ends in shambles for the surgeons when Izzie and George flatline. In a vision, Izzie wears the prom dress that she wore the night Denny died and gets on an elevator with George, who's in a US Army uniform. And we, the viewers, ugly-cry as Greg Laswell's "Off I Go" drowns out our tears.