Waking You Up

John dies and Sherlock blames himself, so much so that the guilt begins to affect his life. However, he keeps getting dreams of John talking to him and assuring him that he's not dead.
Eventually Sherlock doesn't seem to know reality from dreams and everyone around thinks he's crazier than usual.
As it is, Sherlock was in coma for awhile and John, very much alive, had been by his bedside constantly and talking to him in hopes he wakes up.

Inspired by my favorite Futurama episode.