Nicholas Colasanto (Coach) was sick during the entire third season, which would result in his death fifteen episodes in. His weight loss is noticeable beginning with this episode and the next one.
The first episode to credit James Burrows, Glen Charles and Les Charles as Executive Producers, instead of Producers, which would be retained for the rest of the series.
Though never explicitly diagnosed on the show, Diane Chambers is probably manic-depressive, with a mix of narcissistic and histrionic personality disorders. The aged chauffeur alludes to her mother's severe paranoia.
Frasier offers to counsel Sam out of his relapse with alcohol, but, in real life, Kelsey Grammer is the one with alcohol (and drug) problems.