Straight dead is if your HP drops to negative your maximum. If that happened, then I'm afraid yes, Xara is dead. If you didn't drop that far into negative, your HP sets itself to zero and you will begin making death saves (d20 roll at the start of your turn, success on 10+, failure under 9). Fail 3 and you die.
EDIT: You succeeded on the save, so you only took 5 Damage. So you're at 0 HP and you owe me 1 Death Save (an unmodified d20 roll which is what you would have done with your turn this round). Not dead yet, but three failures on Death Saves and you will be (but a party member could, as Zaris did for Kaiakas, stabilize you with a Medicine check or by using a charge on a Herbalism Kit).