I have an extreme fear of dying?

I have such a fear of dying, it's like a phobia. This has been going on for weeks and is consuming my life. I don't fear the actual pain or process, but the fear of nothingness. That I will cease to exist and my conscience will die for eternity, never to come back. It just frightens me so much I feel like I'm living in hell knowing that. Knowing that every breathing, living, touching, feeling being just dies like that. It makes the world seem so utterly hopeless to me and I feel such despair. I have nightmares about dying where everything just blacks out, and becomes nothingness. The fear of me becoming nothing for the rest of eternity.