When the Castaways are rescued and back home, they find they can no longer adjust to being off the island.
The brief appearance by Jim Backus, wracked by Parkinson's Disease, in The Harlem Globetrotters on Gilligan's Island. The rest of the cast is visibly moved when he appears, and some were crying.
Everyone knew it would be one of his last performances, and after filming had finished on that brief scene, the entire cast and crew burst into a spontaneous round of applause for Jim Backus.
And it gets worse. After he finished filming his scene, he turned to Dawn Wells and asked her, "Was I funny?" and she reassured him that he was.
There's a flub in this scene. Natalie Schafer (Mrs. Howell) calls him "Jim" instead of "Thurston". Everyone must've been so happy to see him they didn't notice the slip up, or, more likely, didn't care.