Sheldon sits on the side of couch but not on his usual spot, even though it is vacant, showing how his laid-back persona is unconsciously forcing itself out.
Amy mentions that celebrities "have arranged to die in threes". This is called the 'celebrity death rule of threes' phenomenon, and 2016 was a particularly bad year for it, with David Bowie, Alan Rickman and René Angélil (Céline Dion's husband) all dying in January 2016, and Alan Thicke, George Michael and Carrie Fisher all dying in December 2016.
The tune Sheldon plays on a flugelhorn in his dream is "Feels So Good" by Chuck Mangione. It is the on-hold music from The Graduation Transmission (2015).
When Sheldon calls himself a Caucasian James Earl Jones, he actually misquotes The Empire Strikes Back. The line isn't, "Luke, I am your father," a common misconception; it is "No, I am your father."