After regaining consciousness after he was knocked out in a hunt he realized Michael wasn't inside him anymore. He's broken the locks inside Dean's head and went Chuck knows where.

"Damnit. Damnit!" Dean yelled out.

He'd managed to keep Michael locked inside and now that he was gone Dean was too worried of what the Archangel would do now.

"I let my guard down. This is my fault." He said, full on panic mode. He covered his face with his shaky palms. "It's my fault..." He repeated quietly.