In ST:DS9 S2E04 "Invasive Procedures" (and in other scenes where symbionts are implanted/removed) they imply that a joined Trill that has a symbiont removed will, without doubt, die within a fairly short time. Why is this? How is it that the symbionts can survive without being in a host, but the hosts are killed after symbionts are removed? The symbionts can live in those underground caves on Trill without being in a host.
Jadzia is able to survive the fairly short period of time that Dax is removed, and Verad lives despite having the symbiont implanted and removed (they say because it was implanted for such a short amount of time). Doctor Bashir hints that she will live up to a day or so because she is young and healthy. Why isn't she able to recover from the surgery?
But there seems to be a lot of leeway in this. Is it ever shown exactly why it's so dangerous?