Where everybody knows your name, your diagnosis, and a critical plot point to bring on the fourth act.
Sickbay is the room on a starship where people get liquored up, lights go on that make people talk to themselves, and doctors regularly disclose confidential patient information to whomever might be listening. Some of the expository and consumptive functions of sickbay were later transferred to Ten Forward. (TOS: "The Cardiff Room Bluff", "Was Ever Woman in this Humour Woo'd?"; TNG: "Bringing Up Baby")