"Parallels" is the 11th episode of the 7th season of Star Trek: The Next Generation. Written by Brannon Braga, it first aired on November 29th, 1993.
In the episode, after returning from a tournament involving Klingon combat, Lt. Commander Worf finds himself traveling through different realities--some with subtle differences, others extremely divergent.
Wil Wheaton, who had left the show as a regular earlier in the run of the series, returns in one of the alternate realities.
November 29th, 1993 - Star Trek: The Next Generation's "Parallels" Airs:
They reference a connection to the previous episode "Phantasms" where Data first experiences nightmares. The connection is; one of the "other Enterprises" has the engine core from Data's dreams.