From Chabad.org: The autumn holiday of Sukkot is now introduced. During this seven-day holiday we are commanded to sit in outdoor booths, take the Four Species (citron, palm branch, myrtles, and willows), and rejoice before G‑d. The final holiday is Shemini Atzeret, a one-day holiday which immediately follows Sukkot.
Shmini Atzeret is a very unique and romantic holiday. Rashi explains that G-d doesn’t want us to leave Him after Sukkot, and asks us to stay with Him just one more day. Why is this the only holiday where G-d gets so attached to us that He asks us to stay? Well, it could be that Sukkot is the most all-encompassing holiday we have. Between living and eating in the Sukkah, to shaking the Lulav and Etrog, we perform so many Mitzvot (much of it by design, since we just started a new slate on Yom Kippur 5 days earlier). All that time AND activity together tends to cause separation anxiety, but only if you’ve enjoyed your time together!