"Equilibrium" is the 50th episode of the television series Star Trek: Deep Space Nine, the fourth episode of the third season. Set in the 24th century, the series follows the adventures on Deep Space Nine, a space station located near a stable wormhole between the Alpha and Gamma quadrants of the Milky Way Galaxy, near the planet Bajor. This episode is centered on the Station Ops crew, with several guest stars. It focuses on the Trill character Jadzia Dax and the mysterious occurrences that begin to happen to her. It also further explores the Trill alien species, especially the nature of their "symbionts". It achieved a Nielsen rating of 7.4, which is an estimated percentage of viewership out of the total number of U.S. households. It originally aired in broadcast syndication on October 17, 1994. Background The Trill aliens were introduced on Star Trek: The Next Generation on May 11, 1991, with the episode "The Host". "The Host" was directed by Marvin V. Rush and written by Michel Horvat. They return as one of the prime characters of Deep Space Nine, with Jadzia Dax. Dax is a symbiotic lifeform that is implanted in a living host. The symbiont has the memories of all of its previous hosts, this provides an emotional bonding of personalities linking host and symbiont and can lead to interesting social situations. On Deep Space Nine, Jadzia Dax is a joined Trill (not all Trill have a symbiont - they are rare) and many episodes explore the situation; major Trill episodes prior to "Equilibrium" include "Dax" (S1E8), "Invasive Procedures" (S2E4), and "Blood Oath" (S2E18). Plot At a dinner party, Jadzia Dax toys with a piano and finds herself playing an unfamiliar tune despite having no musical training in this life nor in her previous ones. Later, she experiences odd mood swings and hallucinations of a masked figure. Bashir finds that these symptoms are linked to her symbiont. According to Dax's medical history, a previous host experienced similar symptoms when he went into a six-month coma. Sisko and Bashir take Dax back to her homeworld, where Doctor Renhol of the Trill Symbiosis Commission stabilizes Dax's symptoms. However, Dax suffers a relapse and experiences a new hallucination of Trill hospital guards in century-old uniforms accosting her. Frustrated, Sisko, Bashir, and Dax visit the caves where unjoined symbionts are spawned to consult the caretakers. A caretaker there believes that Dax's