Nostalgia was the attempt to hold on memories, events, and objects from a past timeline.
Spock was unable to understand James T. Kirk's nostalgia for a waterless, barren wasteland when Kirk mentioned his wish to be at a desert with sunlight and palm trees. (TOS: "The Squire of Gothos")
When The Doctor examined Tom Paris following his amnesia, he only found Paris' lapses into nostalgia (which he found irritating) as an unusual test result. Nothing more was wrong with him. (VOY: "Cathexis")
Tuvok mentioned that he was not experiencing feelings of nostalgia but was pleased when he thought back to those days of meeting Kirk, Spock and the others. (VOY: "Flashback")
When Seven of Nine and B'Elanna Torres examined Borg technology in cargo bay 2, Torres suggested nostalgia as the result Seven was experiencing. But Seven turned this possibility down. (VOY: "Survival Instinct")
When Reginald Barclay activated an EMH Mark One, Doctor Lewis Zimmerman mentioned he was not in the mood for nostalgia. (VOY: "Life Line")