Has anyone had a feelilng like they were going to die?

I am having a pretty major surgery on June 3rd, and I have this overwhelming sense of impending doom. I feel like I should write letters to all of my loved ones (and not so loved ones) to say goodbye. I haven't told anyone about this because it makes me sound like I am crazy. I am generally an upbeat, down-to-earth person, and I have had several surgeries in the past without feeling anything like this. I don't feel scared to die, nor do I want to die, but I have a husband and 4 kids who would be greatly affected if I were to die during surgery. Should I fill up a notebook with my thoughts and words, or am I just turning into a nut case?