Abyss

S6, E6: O'Neill (Richard Dean Anderson) flees a Jaffa attack on an unknown planet but is captured alongside a slave before reaching the Stargate. Imprisoned and tortured by Ba'al the System Lord O'Neill loses his memory and cannot remember where he is or why he is there. The specter of Daniel Jackson (Michael Shanks) who has been elevated to another plane of existence in death appears in O'Neill's prison cell and offers the mystical wisdom of Oma. Since SG-1 lacks the firepower to attack Ba'al's fortress Teal'c (Christopher Judge) suggests recruiting one of the other system lords to attack it. O'Neill and the slave escape together as Daniel appears one last time to tell him You're going to be all right.