Resilient ConstructionSource Inner Sea Races pg. 199
You spent a great deal of time around magical workshops, and the power of magic sustains you. Once per day, if you would be reduced to 0 or fewer hit points while under the effects of an ongoing spell you cast with a range of personal, you are not destroyed by the attack, but instead become inactive and helpless for 1 round, at negative hit points. If you take damage again during that time, or if you are still below 0 hit points at the end of that round, you are destroyed.