Beneath the Surface (S04E10)

SG-1 awakens in a mysterious underground complex, with no memory of their previous lives. In fact, they seem to possess a whole new set of memories. No longer Col. Jack O'Neill, Maj. Samantha Carter, Dr. Daniel Jackson, and Teal'c, they are Jonah, Therra, Carlin and Tor, laborers doomed to a dreary existence, working the mines beneath an ice-covered planet. Back at Stargate Command, meanwhile, Gen. Hammond faces the possibility that SG-1 has perished on the planet's icy surface, an outcome he refuses to accept. As the general tries to unravel the team's mysterious disappearance, the members of SG-1 grasp at fleeting memories of their former lives, memories that are not just the keys to their freedom, but to their very survival. (Metro-Goldwyn-Mayer (MGM))