If a Half-Orc is dropped to 0 by an Illithid can it use relentless endurance?

@ChrisPerkinsDnD If a Half-Orc is dropped to 0 by an Illithid's attack, can it use relentless endurance to not have its brain drained?

— Gillian (@JustGillianTime) July 8, 2016

I would say YES because the half-orc doesn't really drop to 0 hit points. It still has 1 hp left. https://t.co/XqCAW3GiJi

— (((Chris Perkins))) (@ChrisPerkinsDnD) July 8, 2016