Doesn't almost everyone have a deep-rooted fear of death? Mine has become dulled of late; over the last couple of years I've been at various points threatened, suicidal and nearly killed by accident, and never once did I feel a twinge of fear, just discomfort at the lack of fear I was feeling. What this trip taught me was that I am concerned, very much, with pain. Yes I was regretting leaving my friends and family behind, ending life so soon when things were starting to get interesting, and probably ceasing to exist altogether, all of which made me feel helpless and frustrated. But the immediate thing that got to me was that I knew how much this was going to hurt. *shrug*
A heart monitor is a good idea, I will invest in that soon if this anxiety returns in future trips.