The Vampire Diaries season 7 episode 10
Episode title: Hell Is Other People
After finding himself on the wrong end of Julian's plan to avenge Lily's death, Damon awakens to find himself trapped inside the Phoenix stone, tormented by a traumatic experience from his time in the Civil War and forced to face his darkest demon in order to get out. On the outside, Bonnie is in a race against the clock to get Damon out before the effects of the Phoenix stone take over and leave him changed forever.
