Dream (Destiel)

Dean falls into a coma, and no one really knows why. Him and Sam were on a job, demon, and suddenly Dean was asleep in an alley.
Castiel discovers he can enter Dean's subconscious, and he finds out that Dean was poisoned by an unheard of Angel, Adonael. Cas spends most of his time in Dean's mind, trying to piece together everything that's happening.
Adonael poisoned Dean to distract Cas, so Adonael could take over Heaven, Earth, and Hell. Cas is coming close to finding out how to pull Dean out, when he's pulled out of Dean's mind.
Cas can't enter Dean's mind anymore, and Dean in pronounced clinically dead, just as Adonael wreaks havoc in Heaven, creating a frenzy up there, as he starts to kill them off, one by one.