Mhm. I think i know what you mean. I had this fear too (is there any i had "not"? lol) when i was younger. The mind just cant handle non-existance, and i believe thats why it creates big fears.
It helps to understand what fear is... the primal, real fear - when you face a big danger, and the fear of events in the past or future, which is created by thoughts/mind.
The second fear is not real, its just one or more thoughts. So its all about letting go of these thoughts.
There are several ways to do this. A very effective would be, to face the thought-created fear, and experience that its not real. This takes the fear away immediately. Another one is to get to the ultimate conclusion, that thought-fears are not real, and to deeply believe it.
Well, im writing a novell... maybe it helps a bit.
Atb,
Phil