It all comes down to sweet memory and its torture for Izzie in the episode called "In the Midnight Hour". This would be the "Grey's Anatomy" episode where Izzie's deceased fiance, Denny Duquette played by Jeffrey Dean Morgan, comes back haunting her.
Months after his death, Izzie was reminded of Denny in episode 5.07 when a patient was treated with similar disease that killed him. Izzie is having visions of him which was speculated as a symptom of Izzie's brain tumor that she will suffer.
Meanwhile, the November 20 episode also sees Meredith, Cristina and Bailey coming to Lexie and Sadie's rescue when a routine surgery goes horribly wrong. As Owen and Derek treat a man seriously injured while sleepwalking and Mark comforts the sleepwalker's distraught daughter. Owen's feeling for Cristina is also given a spotlight here.