What happens to Bilbo at the end of chapter 4?

Great Goblin rushes towards Thorin but the lights go out and white sparks begin to burst, burning holes in the goblins. A sword flashes and kills the Great Goblin, and then a voice says "follow me quick." Bilbo and the others follow Gandalf but he Goblins are in close pursuit and Dori is grabbed from behind. Bilbo falls into blackness, bumps his head on a hard rock and remembers nothing more.